This report presents estimates of the undocumented population residing in the United States in 2018, highlighting demographic changes since 2010. The Center for Migration Studies of New York (CMS) compiled these estimates based primarily on information collected in the US Census Bureau’s American Community Survey (ACS). The annual CMS estimates of undocumented residents for 2010 to 2018 include all the detailed characteristics collected in the ACS.  A summary of the CMS estimation procedures, as well as a discussion of the plausibility of the estimates, is provided in the Appendix.
The total undocumented population in the United States continued to decline in 2018, primarily because large numbers of undocumented residents returned to Mexico. From 2010 to 2018, a total of 2.6 million Mexican nationals left the US undocumented population;  about 1.1 million, or 45 percent of them, returned to Mexico voluntarily. The decline in the US undocumented population from Mexico since 2010 contributed to declines in the undocumented population in many states. Major findings include the following:
- The total US undocumented population was 10.6 million in 2018, a decline of about 80,000 from 2017, and a drop of 1.2 million, or 10 percent, since 2010.
- Since 2010, about two-thirds of new arrivals have overstayed temporary visas and one-third entered illegally across the border.
- The undocumented population from Mexico fell from 6.6 million in 2010 to 5.1 million in 2018, a decline of 1.5 million, or 23 percent.
- Total arrivals in the US undocumented population from El Salvador, Guatemala, and Honduras — despite high numbers of Border Patrol apprehensions of these populations in recent years — remained at about the same level in 2018 as in the previous four years. 
- The total undocumented population in California was 2.3 million in 2018, a decline of about 600,000 compared to 2.9 million in 2010. The number from Mexico residing in the state dropped by 605,000 from 2010 to 2018.
- The undocumented population in New York State fell by 230,000, or 25 percent, from 2010 to 2018. Declines were largest for Jamaica (−51 percent), Trinidad and Tobago (−50 percent), Ecuador (−44 percent), and Mexico (−34 percent).
- The results shown here reinforce the view that improving social and economic conditions in sending countries would not only reduce pressure at the border but also likely cause a large decline in the undocumented population.
- Two countries had especially large population changes — in different directions — in the 2010 to 2018 period. The population from Poland dropped steadily, from 93,000 to 39,000, while the population from Venezuela increased from 65,000 to 172,000. Almost all the increase from Venezuela occurred after 2014.
Undocumented residents can leave that population by voluntary departure, removal by the US Department of Homeland Security (DHS), adjustment to lawful permanent resident (LPR) status, or, in a relatively few cases, dying. The methodology used to estimate departures from the population is described in the Appendix.
Even though total border apprehensions of El Salvadorans, Guatemalans, and Hondurans increased by 63,000 in 2018, from 163,000 to 226,000, total undocumented arrivals from these three countries increased by only 12,000.