The number of illegal immigrants in the United States has not changed significantly since 2005; the Pew Hispanic Center estimated from the March 2005 Current Population Survey and Department of Homeland Security reports that there were between 11.5 and 12 million unauthorized migrants, a number approximating the number of illegal immigrants today.
The number of those immigrants who overstayed their visas plummeted after 9/11, as enhanced security techniques had a profound effect on those who stayed beyond the time limit. The consequences of 9/11 for those who overstayed their visas were logical enough; at least 6 of the 9/11 hijackers were here past the time limit in their visas. The number of immigrants who overstayed their visas sank 73% from 2000-2009.
The number of illegal immigrants soared from 1996 to 2000; in 1996 there were 5 million illegal immigrants in the U.S. According to a paper authored by Robert Warren, who was Director of Statistics at the former Immigration and Naturalization Service, 1986 to 1995, and John Robert Warren, who is with the Minnesota Population Center, Department of Sociology, University of Minnesota, the number of EWI’s (which stands for those who entered without inspection) dropped rapidly every year in every state after 2005 but the number of overstays dropped even more significantly.
Although the number of overstays dropped most precipitously in the years immediately following 9/11, EWI’s dropped from 9/11 to 2003, rose from 2003-2005, then dwindled by two-thirds from 2005-2009.