Estimates derived from the March Supplement of the U.S. Census Bureau's Current Population Survey (CPS) indicate that the unauthorized resident alien population (commonly referred to as illegal aliens) rose from 3.2 million in 1986 to 12.4 million in 2007, before leveling off at 11.1 million in 2011. The estimated number of unauthorized aliens had dropped to 1.9 million in 1988 following passage of a 1986 law that legalized several million unauthorized aliens. Jeffrey Passel, a demographer with the Pew Hispanic Research Center, has been involved in making these estimations since he worked at the U.S. Bureau of the Census in the 1980s.
Similarly, the Department of Homeland Security's Office of Immigration Statistics (OIS) reported an estimated 11.5 million unauthorized alien residents as of January 2011, up from 8.5 million in January 2000. The OIS estimated that the unauthorized resident alien population in the United States increased by 37 percent over the period 2000 to 2008, before leveling off since 2009. The OIS estimated that 6.8 million of the unauthorized alien residents in 2011 were from Mexico. About 33 percent of unauthorized residents in 2011 were estimated to have entered the United States since 2000, but the rate of illegal entry appears to be slowing. The OIS based its estimates on data from the U.S. Census Bureau's American Community Survey.