The term "immigrants" (also known as the foreign born) refers to people residing in the United States who were not U.S. citizens at birth. This population includes naturalized citizens, legal permanent residents, certain legal non-immigrants (e.g., refugees and persons on student or work visas), and persons illegally residing in the United States.
Migration Policy Institute tabulation of data from the U.S. Census Bureau's 2010, 2011, and 2012 American Community Surveys. Data from the 1970, 1990, and 2000 decennial Censuses were accessed from Steven Ruggles, J. Trent Alexander, Katie Genadek, Ronald Goeken, Matthew B. Schroeder, and Matthew Sobek. Integrated Public Use Microdata Series: Version 5.0 [Machine-readable database]. Minneapolis: University of Minnesota, 2010. Data for 1850 to 1990, excluding 1940 and 1950 were from Campbell J. Gibson and Emily Lennon, "Historical Census Statistics on the Foreign-born Population of the United States: 1850-1990," U.S. Census Bureau, Population Division, Working Paper No. 29, February 1999.