The falloff in the stock of unauthorized immigrants has been driven mainly by a decrease in the number of new immigrants from Mexico, the single largest source of U.S. migrants. As the Pew Hispanic Center reported earlier this year, net immigration from Mexico to the United States has stopped and possibly reversed through 2010. At its peak in 2000, about 770,000 immigrants arrived annually from Mexico; the majority arrived illegally. By 2010, the inflow had dropped to about 140,000—a majority of whom arrived as legal immigrants, according to Pew Hispanic Center estimates.
These Pew Hispanic Center estimates use data mainly from the Current Population Survey (CPS), a monthly survey of about 55,000 households conducted jointly by the Bureau of Labor Statistics and the Census Bureau. It is best known as a source for monthly employment statistics.
The Pew Hispanic Center estimates the unauthorized immigrant population using the “residual method,” a well-developed and widely accepted technique that is based on official government data. Under this methodology, a demographic estimate of the legal foreign-born population—naturalized citizens, legal permanent residents, temporary legal residents and refugees—is subtracted from the total foreign-born population. The remainder, or residual, is the source of population estimates and characteristics of unauthorized immigrants.
These data are very important from a policy perspective, as Congress prepares anew to consider immigration reform, and the main author of the report, Dr. Jeffrey Passel, discussed the results recently on NPR.