In 1800, the population of the area of modern-day Slovakia was estimated to be just over two million, a figure which would grow steadily throughout the 19th century as part of the kingdom of Hungary and later under the dual kingdom of Austria-Hungary. This growth would continue even throughout the first half of the 20th century, as the country would largely escape conflict in both the First and Second World Wars. As a result, Slovakia’s population would rise to just under three and a half million by 1950.

Slovakia’s population would begin to rapidly increase in the years following the Second World War, however, as the country would experience both a baby boom and large-scale modernization and industrialization as part of the Czechoslovak Socialist Republic. After slowing somewhat in the late 1960s, population growth would increase once more in the 1970s and 1980s, as Slovakia would become the first of the Soviet republics to begin the “normalization” process of reforms brought about by the Soviet perestroika (restructuring) movement. While population growth would largely flatline following the dissolution of the Soviet Union in 1991, unlike many former Soviet republics who saw their populations decline as net emigration rose, Slovakia’s population has managed to avoid declining, and in the 2010s, has even begun to rise again. As a result, in 2020, Slovakia is estimated to have a population of just under five and a half million.

In the early twentieth century, modern-day Czechia and Slovakia were united, as a part of the Austro-Hungarian Empire until after World War I. It then became an independent state in 1918, although the borders did change during this time and after the Second World War, until it peacefully dissolved into the both Czechia and Slovakia in 1993. The population of Czechoslovakia did not grow significantly between 1910 and 1921, and in regards to gender the male population actually decreased by around 50 thousand. The population drastically decreases from 1930 to 1946/7, from 14.7 to 12.2 million people. These changes are mostly as a result of both World Wars, mass displacement of ethnic Germans following WWII, and the rearranging of Czechoslovakia's borders. After 1946/7 the population grows quite gradually, and is almost reaches it's pre-WWII height again in 1970, with 14.35 million people.