The world's population first reached one billion people in 1805, and reached eight billion in 2022, and will peak at almost 10.2 billion by the end of the century. Although it took thousands of years to reach one billion people, it did so at the beginning of a phenomenon known as the demographic transition; from this point onwards, population growth has skyrocketed, and since the 1960s the population has increased by one billion people every 12 to 15 years. The demographic transition sees a sharp drop in mortality due to factors such as vaccination, sanitation, and improved food supply; the population boom that follows is due to increased survival rates among children and higher life expectancy among the general population; and fertility then drops in response to this population growth. Regional differences The demographic transition is a global phenomenon, but it has taken place at different times across the world. The industrialized countries of Europe and North America were the first to go through this process, followed by some states in the Western Pacific. Latin America's population then began growing at the turn of the 20th century, but the most significant period of global population growth occurred as Asia progressed in the late-1900s. As of the early 21st century, almost two-thirds of the world's population lives in Asia, although this is set to change significantly in the coming decades. Future growth The growth of Africa's population, particularly in Sub-Saharan Africa, will have the largest impact on global demographics in this century. From 2000 to 2100, it is expected that Africa's population will have increased by a factor of almost five. It overtook Europe in size in the late 1990s, and overtook the Americas a few years later. In contrast to Africa, Europe's population is now in decline, as birth rates are consistently below death rates in many countries, especially in the south and east, resulting in natural population decline. Similarly, the population of the Americas and Asia are expected to go into decline in the second half of this century, and only Oceania's population will still be growing alongside Africa. By 2100, the world's population will have over three billion more than today, with the vast majority of this concentrated in Africa. Demographers predict that climate change is exacerbating many of the challenges that currently hinder progress in Africa, such as political and food instability; if Africa's transition is prolonged, then it may result in further population growth that would place a strain on the region's resources, however, curbing this growth earlier would alleviate some of the pressure created by climate change.

Until the 1800s, population growth was incredibly slow on a global level. The global population was estimated to have been around 188 million people in the year 1CE, and did not reach one billion until around 1803. However, since the 1800s, a phenomenon known as the demographic transition has seen population growth skyrocket, reaching eight billion people in 2023, and this is expected to peak at over 10 billion in the 2080s.

The world population surpassed eight billion people in 2022, having doubled from its figure less than 50 years previously. Looking forward, it is projected that the world population will reach nine billion in 2038, and 10 billion in 2060, but it will peak around 10.3 billion in the 2080s before it then goes into decline. Regional variations The global population has seen rapid growth since the early 1800s, due to advances in areas such as food production, healthcare, water safety, education, and infrastructure, however, these changes did not occur at a uniform time or pace across the world. Broadly speaking, the first regions to undergo their demographic transitions were Europe, North America, and Oceania, followed by Latin America and Asia (although Asia's development saw the greatest variation due to its size), while Africa was the last continent to undergo this transformation. Because of these differences, many so-called "advanced" countries are now experiencing population decline, particularly in Europe and East Asia, while the fastest population growth rates are found in Sub-Saharan Africa. In fact, the roughly two billion difference in population between now and the 2080s' peak will be found in Sub-Saharan Africa, which will rise from 1.2 billion to 3.2 billion in this time (although populations in other continents will also fluctuate). Changing projections The United Nations releases their World Population Prospects report every 1-2 years, and this is widely considered the foremost demographic dataset in the world. However, recent years have seen a notable decline in projections when the global population will peak, and at what number. Previous reports in the 2010s had suggested a peak of over 11 billion people, and that population growth would continue into the 2100s, however a sooner and shorter peak is now projected. Reasons for this include a more rapid population decline in East Asia and Europe, particularly China, as well as a prolonged development arc in Sub-Saharan Africa.

Between 1800 and 2021, the total population of each continent experienced consistent growth, however as growth rates varied by region, population distribution has fluctuated. In the early 19th century, almost 70 percent of the world's population lived in Asia, while fewer than 10 percent lived in Africa. By the end of this century, it is believed that Asia's share will fall to roughly 45 percent, while Africa's will be on course to reach 40 percent. 19th and 20th centuries Fewer than 2.5 percent of the world's population lived in the Americas in 1800, however the demographic transition, along with waves of migration, would see this share rise to almost 10 percent a century later, peaking at almost 14 percent in the 1960s. Europe's share of the global population also grew in the 19th century, to roughly a quarter in 1900, but fell thereafter and saw the largest relative decline during the 20th century. Asia, which has consistently been the world's most populous continent, saw its population share drop by the mid-1900s, but it has been around 60 percent since the 1970s. It is important to note that the world population has grown from approximately one to eight billion people between 1800 and the 2020s, and that declines in population distribution before 2020 have resulted from different growth rates across the continents. 21st century Africa's population share remained fairly constant throughout this time, fluctuating between 7.5 and 10 percent until the late-1900s, but it is set to see the largest change over the 21st century. As Europe's total population is now falling, and it is estimated that the total populations of Asia and the Americas will fall by the 2050s and 2070s respectively, rapid population growth in Africa will see a significant shift in population distribution. Africa's population is predicted to grow from 1.3 to 3.9 billion people over the next eight decades, and its share of the total population will rise to almost 40 percent. The only other continent whose population will still be growing at this time will be Oceania, although its share of the total population has never been more than 0.7 percent.

In the past four centuries, the population of the Thirteen Colonies and United States of America has grown from a recorded 350 people around the Jamestown colony in Virginia in 1610, to an estimated 346 million in 2025. While the fertility rate has now dropped well below replacement level, and the population is on track to go into a natural decline in the 2040s, projected high net immigration rates mean the population will continue growing well into the next century, crossing the 400 million mark in the 2070s. Indigenous population Early population figures for the Thirteen Colonies and United States come with certain caveats. Official records excluded the indigenous population, and they generally remained excluded until the late 1800s. In 1500, in the first decade of European colonization of the Americas, the native population living within the modern U.S. borders was believed to be around 1.9 million people. The spread of Old World diseases, such as smallpox, measles, and influenza, to biologically defenseless populations in the New World then wreaked havoc across the continent, often wiping out large portions of the population in areas that had not yet made contact with Europeans. By the time of Jamestown's founding in 1607, it is believed the native population within current U.S. borders had dropped by almost 60 percent. As the U.S. expanded, indigenous populations were largely still excluded from population figures as they were driven westward, however taxpaying Natives were included in the census from 1870 to 1890, before all were included thereafter. It should be noted that estimates for indigenous populations in the Americas vary significantly by source and time period. Migration and expansion fuels population growth The arrival of European settlers and African slaves was the key driver of population growth in North America in the 17th century. Settlers from Britain were the dominant group in the Thirteen Colonies, before settlers from elsewhere in Europe, particularly Germany and Ireland, made a large impact in the mid-19th century. By the end of the 19th century, improvements in transport technology and increasing economic opportunities saw migration to the United States increase further, particularly from southern and Eastern Europe, and in the first decade of the 1900s the number of migrants to the U.S. exceeded one million people in some years. It is also estimated that almost 400,000 African slaves were transported directly across the Atlantic to mainland North America between 1500 and 1866 (although the importation of slaves was abolished in 1808). Blacks made up a much larger share of the population before slavery's abolition. Twentieth and twenty-first century The U.S. population has grown steadily since 1900, reaching one hundred million in the 1910s, two hundred million in the 1960s, and three hundred million in 2007. Since WWII, the U.S. has established itself as the world's foremost superpower, with the world's largest economy, and most powerful military. This growth in prosperity has been accompanied by increases in living standards, particularly through medical advances, infrastructure improvements, clean water accessibility. These have all contributed to higher infant and child survival rates, as well as an increase in life expectancy (doubling from roughly 40 to 80 years in the past 150 years), which have also played a large part in population growth. As fertility rates decline and increases in life expectancy slows, migration remains the largest factor in population growth. Since the 1960s, Latin America has now become the most common origin for migrants in the U.S., while immigration rates from Asia have also increased significantly. It remains to be seen how immigration restrictions of the current administration affect long-term population projections for the United States.

The earliest point where scientists can make reasonable estimates for the population of global regions is around 10,000 years before the Common Era (or 12,000 years ago). Estimates suggest that Asia has consistently been the most populated continent, and the least populated continent has generally been Oceania (although it was more heavily populated than areas such as North America in very early years). Population growth was very slow, but an increase can be observed between most of the given time periods. There were, however, dips in population due to pandemics, the most notable of these being the impact of plague in Eurasia in the 14th century, and the impact of European contact with the indigenous populations of the Americas after 1492, where it took almost four centuries for the population of Latin America to return to its pre-1500 level. The world's population first reached one billion people in 1803, which also coincided with a spike in population growth, due to the onset of the demographic transition. This wave of growth first spread across the most industrially developed countries in the 19th century, and the correlation between demographic development and industrial or economic maturity continued until today, with Africa being the final major region to begin its transition in the late-1900s.

The Anthropogenic Biomes of the World, Version 2: 1800 data set describes anthropogenic transformations within the terrestrial biosphere caused by sustained direct human interaction with ecosystems, including agriculture and urbanization c. 1800. Potential natural vegetation, biomes, such as tropical rainforests or grasslands, are based on global vegetation patterns related to climate and geology. Anthropogenic transformation within each biome is approximated using population density, agricultural intensity (cropland and pasture) and urbanization. This data set is part of a time series for the years 1800, 1800, 1900, and 2000 that provides global patterns of historical transformation of the terrestrial biosphere during the Industrial Revolution.

In 2025, India overtook China as the world's most populous country and now has almost 1.46 billion people. China now has the second-largest population in the world, still with just over 1.4 billion inhabitants, however, its population went into decline in 2023. Global population As of 2025, the world's population stands at almost 8.2 billion people and is expected to reach around 10.3 billion people in the 2080s, when it will then go into decline. Due to improved healthcare, sanitation, and general living conditions, the global population continues to increase; mortality rates (particularly among infants and children) are decreasing and the median age of the world population has steadily increased for decades. As for the average life expectancy in industrial and developing countries, the gap has narrowed significantly since the mid-20th century. Asia is the most populous continent on Earth; 11 of the 20 largest countries are located there. It leads the ranking of the global population by continent by far, reporting four times as many inhabitants as Africa. The Demographic Transition The population explosion over the past two centuries is part of a phenomenon known as the demographic transition. Simply put, this transition results from a drastic reduction in mortality, which then leads to a reduction in fertility, and increase in life expectancy; this interim period where death rates are low and birth rates are high is where this population explosion occurs, and population growth can remain high as the population ages. In today's most-developed countries, the transition generally began with industrialization in the 1800s, and growth has now stabilized as birth and mortality rates have re-balanced. Across less-developed countries, the stage of this transition varies; for example, China is at a later stage than India, which accounts for the change in which country is more populous - understanding the demographic transition can help understand the reason why China's population is now going into decline. The least-developed region is Sub-Saharan Africa, where fertility rates remain close to pre-industrial levels in some countries. As these countries transition, they will undergo significant rates of population growth.

Brazil and the United States are the two most populous countries in the Americas today. In 1500, the year that Pedro Álvares Cabral made landfall in present-day Brazil and claimed it for the Portuguese crown, it is estimated that there were roughly one million people living in the region. Some estimates for the present-day United States give a population of two million in the year 1500, although estimates vary greatly. By 1820, the population of the U.S. was still roughly double that of Brazil, but rapid growth in the 19th century would see it grow 4.5 times larger by 1890, before the difference shrunk during the 20th century. In 2024, the U.S. has a population over 340 million people, making it the third most populous country in the world, while Brazil has a population of almost 218 million and is the sixth most populous. Looking to the future, population growth is expected to be lower in Brazil than in the U.S. in the coming decades, as Brazil's fertility rates are already lower, and migration rates into the United States will be much higher. Historical development The indigenous peoples of present-day Brazil and the U.S. were highly susceptible to diseases brought from the Old World; combined with mass displacement and violence, their population growth rates were generally low, therefore migration from Europe and the import of enslaved Africans drove population growth in both regions. In absolute numbers, more Europeans migrated to North America than Brazil, whereas more slaves were transported to Brazil than the U.S., but European migration to Brazil increased significantly in the early 1900s. The U.S. also underwent its demographic transition much earlier than in Brazil, therefore its peak period of population growth was almost a century earlier than Brazil. Impact of ethnicity The demographics of these countries are often compared, not only because of their size, location, and historical development, but also due to the role played by ethnicity. In the mid-1800s, these countries had the largest slave societies in the world, but a major difference between the two was the attitude towards interracial procreation. In Brazil, relationships between people of different ethnic groups were more common and less stigmatized than in the U.S., where anti-miscegenation laws prohibited interracial relationships in many states until the 1960s. Racial classification was also more rigid in the U.S., and those of mixed ethnicity were usually classified by their non-white background. In contrast, as Brazil has a higher degree of mixing between those of ethnic African, American, and European heritage, classification is less obvious, and factors such as physical appearance or societal background were often used to determine racial standing. For most of the 20th century, Brazil's government promoted the idea that race was a non-issue and that Brazil was racially harmonious, but most now acknowledge that this actually ignored inequality and hindered progress. Racial inequality has been a prevalent problem in both countries since their founding, and today, whites generally fare better in terms of education, income, political representation, and even life expectancy. Despite this adversity, significant progress has been made in recent decades, as public awareness of inequality has increased, and authorities in both countries have made steps to tackle disparities in areas such as education, housing, and employment.

Until the 19th century, population growth across the globe was incredibly low. In the first millennium of the Common Era, the world's population grew by an average of just 0.02 percent each year. In Western Europe and Asia, the populations on either side of the millennium were almost the exact same. It was only in the centuries that followed where population growth began to increase, however it was still very low until the 1800s.

Beginning in the 19th century, a phenomenon known as the demographic transition took place, and the world's population began to grow exponentially. The population of the Americas in particular saw the highest average growth rates in these years, due to the high levels of migration and their smaller starting population size in 1820 compared to most other regions. Overall, the average global population growth rate in the period between 1820 and 1998 was roughly six times higher than the preceding eight centuries, and almost 50 times higher than the millennium before that.

Labour Relations in Venice: 1500, 1650, 1800

An abridged data format, created by Daan Jansen (IISH) and continuing on earlier work by Joris Kok (IISH), is being offered as an alternative in October 2020. This new version of the dataset includes only records that contain labour relations, leaving out all population data. This update also involved (depending on the dataset in question, substantial) data cleaning, separating male and female individuals, and removing any duplicate records. Hence, the aggregated number of people mentioned in these updated datasets should equal the total population.

Labour Relations in Spain: 1800, 1900, 2000

An abridged data format, created by Daan Jansen (IISH) and continuing on earlier work by Joris Kok (IISH), is being offered as an alternative in October 2020. This new version of the dataset includes only records that contain labour relations, leaving out all population data. This update also involved (depending on the dataset in question, substantial) data cleaning, separating male and female individuals, and removing any duplicate records. Hence, the aggregated number of people mentioned in these updated datasets should equal the total population.

Labour Relations in the United States: 1800

An abridged data format, created by Daan Jansen (IISH) and continuing on earlier work by Joris Kok (IISH), is being offered as an alternative in October 2020. This new version of the dataset includes only records that contain labour relations, leaving out all population data. This update also involved (depending on the dataset in question, substantial) data cleaning, separating male and female individuals, and removing any duplicate records. Hence, the aggregated number of people mentioned in these updated datasets should equal the total population.

Labour Relations in Brazil: 1650, 1800

An abridged data format, created by Daan Jansen (IISH) and continuing on earlier work by Joris Kok (IISH), is being offered as an alternative in October 2020. This new version of the dataset includes only records that contain labour relations, leaving out all population data. This update also involved (depending on the dataset in question, substantial) data cleaning, separating male and female individuals, and removing any duplicate records. Hence, the aggregated number of people mentioned in these updated datasets should equal the total population.

The history of modern Brazil begins in the year 1500 when Pedro Álvares Cabral arrived with a small fleet and claimed the land for the Portuguese Empire. With the Treaty of Torsedillas in 1494, Spain and Portugal agreed to split the New World peacefully, thus allowing Portugal to take control of the area with little competition from other European powers. As the Portuguese did not arrive with large numbers, and the indigenous population was overwhelmed with disease, large numbers of African slaves were transported across the Atlantic and forced to harvest or mine Brazil's wealth of natural resources. These slaves were forced to work in sugar, coffee and rubber plantations and gold and diamond mines, which helped fund Portuguese expansion across the globe. In modern history, transatlantic slavery brought more Africans to Brazil than any other country in the world. This combination of European, African and indigenous peoples set the foundation for what has become one of the most ethnically diverse countries across the globe.

Independence and Monarchy By the early eighteenth century, Portugal had established control over most of modern-day Brazil, and the population more than doubled in each half of the 1800s. The capital of the Portuguese empire was moved to Rio de Janeiro in 1808 (as Napoleon's forces moved closer towards Lisbon), making this the only time in European history where a capital was moved to another continent. The United Kingdom of Portugal, Brazil and the Algarves was established in 1815, and when the Portuguese monarchy and capital returned to Lisbon in 1821, the King's son, Dom Pedro, remained in Brazil as regent. The following year, Dom Pedro declared Brazil's independence, and within three years, most other major powers (including Portugal) recognized the Empire of Brazil as an independent monarchy and formed economic relations with it; this was a much more peaceful transition to independence than many of the ex-Spanish colonies in the Americas. Under the reign of Dom Pedro II, Brazil's political stability remained relatively intact, and the economy grew through its exportation of raw materials and economic alliances with Portugal and Britain. Despite pressure from political opponents, Pedro II abolished slavery in 1850 (as part of a trade agreement with Britain), and Brazil remained a powerful, stable and progressive nation under Pedro II's leadership, in stark contrast to its South American neighbors. The booming economy also attracted millions of migrants from Europe and Asia around the turn of the twentieth century, which has had a profound impact on Brazil's demography and culture to this day.

The New Republic

Despite his popularity, King Pedro II was overthrown in a military coup in 1889, ending his 58 year reign and initiating six decades of political instability and economic difficulties. A series of military coups, failed attempts to restore stability, and the decline of Brazil's overseas influence contributed greatly to a weakened economy in the early 1900s. The 1930s saw the emergence of Getúlio Vargas, who ruled as a fascist dictator for two decades. Despite a growing economy and Brazil's alliance with the Allied Powers in the Second World War, the end of fascism in Europe weakened Vargas' position in Brazil, and he was eventually overthrown by the military, who then re-introduced democracy to Brazil in 1945. Vargas was then elected to power in 1951, and remained popular among the general public, however political opposition to his beliefs and methods led to his suicide in 1954. Further political instability ensued and a brutal, yet prosperous, military dictatorship took control in the 1960s and 1970s, but Brazil gradually returned to a democratic nation in the 1980s. Brazil's economic and political stability fluctuated over the subsequent four decades, and a corruption scandal in the 2010s saw the impeachment of President Dilma Rousseff. Despite all of this economic instability and political turmoil, Brazil is one of the world's largest economies and is sometimes seen as a potential superpower. The World Bank classifies it as a upper-middle income country and it has the largest share of global wealth in Latin America. It is the largest Lusophone (Portuguese-speaking), and sixth most populous country in the world, with a population of more than 210 million people.

Until 2007, the share of the global population living in urban areas was always smaller than the rural population, but in 2021, the world's level of urbanization has risen to around 56 percent, and by 2050, it is estimated that two thirds of the world will live in urban areas. Urbanization on such a large scale is a relatively new phenomenon, and has a strong correlation with the industrial maturity of a society. For most of pre-industrial times, fewer than five percent of the total population lived in urban centers, which were generally trading and administrative centers. The main reason for this was the agricultural demands of the time, where subsistence farming was the primary method of food production for the general population. Compared to Japan and China, a larger share of Western Europe lived in urban centers in the 16th century, due to higher levels of trade along the Mediterranean and between northern states, but around 94 percent of the population still lived in a rural setting. Effect of industrialization With the onset of the first industrial revolution in the 19th century, the mechanization of agriculture and development of manufacturing industries saw a shift in labor demands in Western Europe. People began migrating to cities on a large scale, and migration to the U.S. also increased due to industrialization in the northeastern states. Urban populations then became more prosperous, although mortality rates were initially higher due to the more rapid spread of disease and poor sanitation infrastructure. This mortality also disproportionately affected children and more recent arrivals. Global trends Waves of industrialization in Europe saw further urbanization throughout the 1800s, and roughly a third of the population had urbanized by the end of the 19th century. Globally, it would take until the 1960s before one third of the population had urbanized, and it was not until the late 1990s where China's urbanization rate had reached this level. However, China's urbanization rate has grown rapidly since the 1980s, and is now around 80 percent of the EU's level, whereas it was closer to 50 percent just two decades previously. Japan's urbanization rate was comparable to Europe's for most of the 20th century, but increased further throughout the 2010s; today it has one of the highest rates among more developed nations, although this has presented some challenges for Japanese society.

Labour Relations in Taiwan: 1500, 1650, 1800

An abridged data format, created by Daan Jansen (IISH) and continuing on earlier work by Joris Kok (IISH), is being offered as an alternative in October 2020. This new version of the dataset includes only records that contain labour relations, leaving out all population data. This update also involved (depending on the dataset in question, substantial) data cleaning, separating male and female individuals, and removing any duplicate records. Hence, the aggregated number of people mentioned in these updated datasets should equal the total population.

Labour Relations in Java (Indonesia): 1650, 1800, 1900

An abridged data format, created by Daan Jansen (IISH) and continuing on earlier work by Joris Kok (IISH), is being offered as an alternative in October 2020. This new version of the dataset includes only records that contain labour relations, leaving out all population data. This update also involved (depending on the dataset in question, substantial) data cleaning, separating male and female individuals, and removing any duplicate records. Hence, the aggregated number of people mentioned in these updated datasets should equal the total population.

During the eighteenth century, it is estimated that France's population grew by roughly fifty percent, from 19.7 million in 1700, to 29 million by 1800. In France itself, the 1700s are remembered for the end of King Louis XIV's reign in 1715, the Age of Enlightenment, and the French Revolution. During this century, the scientific and ideological advances made in France and across Europe challenged the leadership structures of the time, and questioned the relationship between monarchial, religious and political institutions and their subjects. France was arguably the most powerful nation in the world in these early years, with the second largest population in Europe (after Russia); however, this century was defined by a number of costly, large-scale conflicts across Europe and in the new North American theater, which saw the loss of most overseas territories (particularly in North America) and almost bankrupted the French crown. A combination of regressive taxation, food shortages and enlightenment ideologies ultimately culminated in the French Revolution in 1789, which brought an end to the Ancien Régime, and set in motion a period of self-actualization.

War and peace

After a volatile and tumultuous decade, in which tens of thousands were executed by the state (most infamously: guillotined), relative stability was restored within France as Napoleon Bonaparte seized power in 1799, and the policies of the revolution became enforced. Beyond France's borders, the country was involved in a series of large scale wars for two almost decades, and the First French Empire eventually covered half of Europe by 1812. In 1815, Napoleon was defeated outright, the empire was dissolved, and the monarchy was restored to France; nonetheless, a large number of revolutionary and Napoleonic reforms remained in effect afterwards, and the ideas had a long-term impact across the globe. France experienced a century of comparative peace in the aftermath of the Napoleonic Wars; there were some notable uprisings and conflicts, and the monarchy was abolished yet again, but nothing on the scale of what had preceded or what was to follow. A new overseas colonial empire was also established in the late 1800s, particularly across Africa and Southeast Asia. Through most of the eighteenth and nineteenth century, France had the second largest population in Europe (after Russia), however political instability and the economic prioritization of Paris meant that the entire country did not urbanize or industrialize at the same rate as the other European powers. Because of this, Germany and Britain entered the twentieth century with larger populations, and other regions, such as Austria or Belgium, had overtaken France in terms of industrialization; the German annexation of Alsace-Lorraine in the Franco-Prussian War was also a major contributor to this.

World Wars and contemporary France

Coming into the 1900s, France had a population of approximately forty million people (officially 38 million* due to to territorial changes), and there was relatively little growth in the first half of the century. France was comparatively unprepared for a large scale war, however it became one of the most active theaters of the First World War when Germany invaded via Belgium in 1914, with the ability to mobilize over eight million men. By the war's end in 1918, France had lost almost 1.4 million in the conflict, and approximately 300,000 in the Spanish Flu pandemic that followed. Germany invaded France again during the Second World War, and occupied the country from 1940, until the Allied counter-invasion liberated the country during the summer of 1944. France lost around 600,000 people in the course of the war, over half of which were civilians. Following the war's end, the country experienced a baby boom, and the population grew by approximately twenty million people in the next fifty years (compared to just one million in the previous fifty years). Since the 1950s, France's economy quickly grew to be one of the strongest in the world, despite losing the vast majority of its overseas colonial empire by the 1970s. A wave of migration, especially from these former colonies, has greatly contributed to the growth and diversity of France's population today, which stands at over 65 million people in 2020.

The RCS-Dem dataset reports estimates of religious demographics, both country by country and region by region. RCS was created to fulfill the unmet need for a dataset on the religious dimensions of countries of the world, with the state-year as the unit of observation. It covers 220 independent states, 26 selected substate entities, and 41 geographically separated dependencies, for every year from 2015 back to 1900 and often 1800 (more than 42,000 state-years). It estimates populations and percentages of adherents of 100 religious denominations including second level subdivisions within Christianity and Islam, along with several complex categories such as "Western Christianity." RCS is designed for easy merger with datasets of the Correlates of War and Polity projects, datasets by the United Nations, the Religion And State datasets by Jonathan Fox, and the ARDA national profiles.