Estimates of the Illegal Alien Population Residing in the United States: January 2015 [open pdf - 563KB]
From the Document: "This report provides estimates of the size of the illegal alien population residing in the United States as of January 2015 by period of entry, region and country of origin, state of residence, age, and sex. The estimates were derived using the residual methodology employed for previous estimates of this population. The illegal alien population is the remainder (or residual) after the legally resident foreign-born population-- naturalized citizens, lawful permanent residents (LPRs), asylees, refugees, and nonimmigrants--is subtracted from the total foreign-born population. Data to estimate the legally resident foreign-born population were obtained primarily from the Department of Homeland Security (DHS), and estimates of the total foreign-born population were derived from the American Community Survey (ACS) of the U.S. Census Bureau."
Department of Homeland Security: http://www.dhs.gov/