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, lawful permanent residents (LPRs), certain legal nonimmigrants (e.g., persons on student or work visas), those admitted under refugee or asylee status, and persons illegally residing in the United States.
Migration Policy Institute tabulation of data from the U.S. Census Bureau's 2010 - 2013 American Community Surveys and 1970, 1990, and 2000 decennial Census data. All other data are from Campbell J. Gibson and Emily Lennon, "Historical Census Statistics on the Foreign-Born Population of the United States: 1850 to 1990" (Working Paper no. 29., U.S. Census Bureau, Washington, DC, 1999).