As of 2010, just over 40 million people living in the United States were born in another country, and of those, an estimated 11 million came here illegally. That's down from a peak of 12 million in 2007.
Well over half of unauthorized immigrants were born in Mexico, and their population is most heavily concentrated along the southwest border.
About the Data
These estimates were produced by Jeffrey Passel and D’Vera Cohn of the Pew Hispanic Center for a 2011 report. Passel and Cohn use what is called the “residual method” for estimating the unauthorized population, subtracting a demographic estimate of the legal foreign-born population from the total foreign-born population.
The source of their data is the expanded March version of the monthly Current Population Survey, conducted by the Bureau of Labor Statistics and the Census Bureau. The authors made adjustments the government data to compensate for undercounting of some groups. For some smaller states with larger sampling variability, state estimates shown above are based on an average of 2009 and 2010 data.