The estimated population of unauthorized immigrants in the U.S. stands at around ** million people. Although the number has stabilized, the United States has seen a spike in migrant encounters in the last few years, with over * million cases registered by the U.S. Border Patrol in 2023. This is a slight decrease from the previous year, when there were over *** million cases registered. Due to its proximity and shared border, Mexico remains the leading country of origin for most undocumented immigrants in the U.S., with California and Texas being home to the majority.

Immigration and political division

Despite the majority of the population having immigrant roots, the topic of immigration in the U.S. remains one of the country’s longest-standing political debates. Support among Republicans for restrictive immigration has grown alongside Democratic support for open immigration. This growing divide has deepened the polarization between the two major political parties, stifling constructive dialogue and impeding meaningful reform efforts and as a result, has led to dissatisfaction from all sides. In addition to general immigration policy, feelings toward illegal immigration in the U.S. also vary widely. For some, it's seen as a significant threat to national security, cultural identity, and economic stability. This perspective often aligns with support for stringent measures like Trump's proposed border wall and increased enforcement efforts. On the other hand, there are those who are more sympathetic toward undocumented immigrants, as demonstrated by support for the Deferred Action for Childhood Arrivals (DACA) program.

The Bureau of Transportation Statistics (BTS) Border Crossing Data provide summary statistics for inbound crossings at the U.S.-Canada and the U.S.-Mexico border at the port level. Data are available for trucks, trains, containers, buses, personal vehicles, passengers, and pedestrians. Border crossing data are collected at ports of entry by U.S. Customs and Border Protection (CBP). The data reflect the number of vehicles, containers, passengers or pedestrians entering the United States. CBP does not collect comparable data on outbound crossings. Users seeking data on outbound counts may therefore want to review data from individual bridge operators, border state governments, or the Mexican and Canadian governments.

In the fiscal year of 2020, the United States Border Patrol apprehended ******* people trying to cross the Southwest border. This was a significant decrease from the previous year, when there were ******* apprehensions by Border Patrol at the Southwest border. This decrease is likely due to the impact of the coronavirus (COVID-19) pandemic.

Significantly more men were apprehended by the United States Border Patrol than women in the the fiscal year of 2020. Nationwide, ******* men were apprehended by Border Patrol in that year, compared to ****** women who were apprehended.

This data package includes the underlying data to replicate the charts and calculations presented in The effect of lawful crossing on unlawful crossing at the US southwest border, PIIE Working Paper 24-10.

If you use the data, please cite as: Clemens, Michael A. 2024. The effect of lawful crossing on unlawful crossing at the US southwest border. PIIE Working Paper 24-10. Washington: Peterson Institute for International Economics.

As of February 2024, almost two-thirds of adults in the United States supported the southern border shutting down to new entrants in the instance that more than five thousand daily attempts were made to cross the border illegally.

In 2024, ** percent of migrants who arrived illegally through Spain's southern border were male adults. Undocumented arrivals of minors accounted for approximately **** percent of all cases, whereas women accounted another **** percent of the total number of irregular immigrants.