Estimates of the Unauthorized Immigrant Population Residing in the United States: January 2009 [open pdf - 418KB]
"This report provides estimates of the number of unauthorized immigrants residing in the United States as of January 2009 by period of entry, region and country of origin, state of residence, age, and gender. The estimates were obtained using the 'residual' methodology employed for estimates of the unauthorized population in 2008 (see Hoefer, Rytina, and Baker, 2009). The unauthorized resident population is the remainder or 'residual' after estimates of the legally resident foreign-born population -- legal permanent residents (LPRs), asylees, refugees, and nonimmigrants -- are subtracted from estimates of the total foreign-born population. Data to estimate the legally resident population were obtained primarily from the Department of Homeland Security (DHS) while the American Community Survey (ACS) of the U.S. Census Bureau was the source for estimates of the total foreign-born population."
Department of Homeland Security: http://www.dhs.gov/index.shtm