Unauthorized Aliens Residing in the United States: Estimates Since 1986
Estimates derived from the March Supplement of the U.S. Census Bureau's Current Population Survey indicate that the unauthorized resident alien population (undocumented immigrants) rose from 3.2 million in 1986 to 12.4 million in 2007 before leveling off at 11.1 million in 2011.
The Department of Homeland Security's Office of Immigration Statistics (OIS) estimated that the undocumented immigrant population increased by 37% over the period 2000 to 2008 before leveling off since 2009. The OIS estimated that 6.8 million of the undocumented immigrants in 2011 were from Mexico. About 33% of undocumented immigrants in 2011 were estimated to have entered the United States since 2000 but the rate of illegal entry appears to be slowing.
Although increased border security, a record number of removals and high unemployment have depressed the levels of illegal migration in recent years, the number of undocumented immigrants residing remains sizeable. Research suggests that various factors have contributed to the ebb and flow of undocumented immigrants and that the increase is often attributed to the "push-pull" of prosperity-fueled job opportunities in the United States in contrast to limited job opportunities in the sending countries. Accordingly, the economic recession that began in December 2007 may have curbed the migration of undocumented immigrants particularly because sectors that traditionally rely on undocumented immigrants, such as construction, services and hospitality, had been especially hard hit.
Wasem, R. E. (2012). Unauthorized Aliens Residing in the United States: Estimates Since 1986. CRS Report for Congress 7-5700. Washington, D.C.: Congressional Research Service. Retrieved from https://sgp.fas.org/crs/misc/RL33874.pdf