Explainer: Illegal Immigration in the United States

Experts inside and outside the U.S. government largely agree that there are between 11 million and 12 million unauthorized immigrants living in the United States, a population that has been essentially flat for the last decade. The unauthorized population rose relatively steadily for decades until peaking at about 12 million in 2007-08, and then held steady or even fell during and after the Great Recession, based on estimates by the three organizations that regularly make these calculations: the Department of Homeland Security (DHS), the Pew Research Center, and the Center for Migration Studies of New York.

U.S. Unauthorized Immigrant Population Estimates, 2000-17

Sources: Bryan Baker, Illegal Alien Population Residing in the United States: January 2015 (Washington, DC: Department of Homeland Security, 2018), available online;  Jeffrey S. Passel and D'Vera Cohn, U.S. Unauthorized Immigrant Total Dips to Lowest Level in a Decade (Washington, DC: Pew Research Center, 2018), available online; Robert Warren, Sharp Multiyear Decline in Undocumented Immigration Suggests Progress at US-Mexico Border, Not a National Emergency (Washington, DC: Center for Migration Studies of New York, 2019), available online.

The Era of Mass Illegal Migration from Mexico Is Over

For decades, illegal immigration was largely a Mexican phenomenon, particularly young men coming for jobs. But this trend has ended for several reasons:

• Mexico has undergone a quiet but major transformation, including declining birth rates and improving economic and educational prospects that have lessened the pressures to migrate for better opportunities
• Mexicans living illegally in the United States, along with Central Americans, have been the overwhelming targets for U.S. immigration enforcement
• The U.S. government has hardened the border, particularly since the 9/11 attacks, and in recent years has significantly increased the penalties for crossing the border illegally.

The result has been that more Mexicans are leaving the United States than are seeking to enter. Between 2007 and 2014, the number of unauthorized Mexican immigrants fell by more than 1 million. The 2008-09 recession cut back on U.S. job opportunities for Mexicans who had immigrated mainly for economic reasons, removing one of the main pull factors. Even as the U.S. economy recovered, though, Mexicans did not return at their earlier pace. In 2018, the U.S. Border Patrol made 152,000 apprehensions of Mexicans trying to cross the border illegally—less than one-tenth the 1.6 million such arrests that occurred during the peak year of 2000.

In the period between 2009 and 2014, 130,000 more Mexican immigrants returned to Mexico than came to the United States. By comparison, between 1995 and 2000, 2.3 million more Mexicans came to the United States than returned to Mexico.

Overall, apprehensions at the U.S.-Mexico border in 2018 were a fraction of their peak, with the 396,579 apprehensions recorded just one-fourth of the nearly 1.65 million that were carried out in 2000.

Changing Face of Illegal Immigration

While the number of Mexican unauthorized immigrants living in the United States has been falling, illegal immigration from other countries has been rising, particularly from Central America and Asia. While Asian unauthorized immigrants typically first arrive legally and then overstay a visa, Central Americans mainly arrive at the U.S.-Mexico border, either attempting to cross illegally or turning themselves in to officers to seek asylum. Apprehensions of migrants from the Northern Triangle of Central America (El Salvador, Guatemala, and Honduras) increased nearly 400 percent between 2008 and 2018. In fiscal year 2018, 56 percent of apprehensions at the Southwest border were of migrants from the Northern Triangle (see animation).

Note: Figures may not add up to 100 percent due to rounding.
Sources: Department of Homeland Security (DHS), Department of Homeland Security Border Security Metrics Report (Washington, DC: DHS, 2018), available online; U.S. Customs and Border Protection, “U.S. Border Patrol Nationwide Apprehensions by Citizenship and Sector, FY2007- FY2018,” accessed April 19, 2019, available online.

Although most Central Americans arriving at the border have been single adults, the flow in recent years increasingly has included significant numbers of unaccompanied children and parents traveling with young children. Central American arrivals at the U.S.-Mexico border have increased since 2013 for a mix of reasons. In general, Central American migration stems from a combination of factors, including violence, insecurity, poverty, and lack of opportunity at home, along with social networks and economic opportunity in the United States. Smuggling networks have also been adept at creating new markets in Central America. The difficulty for U.S. policymakers, who built an enforcement system at the U.S.-Mexico border to confront illegal immigration from Mexico that was overwhelmingly economic in nature, is how to address these new, “mixed” flows of humanitarian and economic migrants.

A Snapshot of the Unauthorized Population

Who makes up the unauthorized population in the United States? MPI has published a demographic snapshot of this population, drawing on analysis of U.S. Census Bureau data, and has a really useful data tool with profiles of the unauthorized at U.S., state, and top county levels.

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