Unauthorized Aliens in the United States: Estimates Since 1986 [September 15, 2004] [open pdf - 40KB]
"This report presents data estimating the number of unauthorized aliens who have been living in the United States since 1986. There have been a variety of estimates of the unauthorized resident alien population over this period, sometimes with substantially different results. This report is limited to data analysis of the Current Population Survey (CPS) conducted by the U.S. Bureau of the Census and the Bureau of Labor Statistics so that there is a basic standard of comparison over time."
CRS Report for Congress, RS21938
Congressional Research Service: http://www.crs.gov