Information on place of birth and citizenship status was used to classify the population into two major categories: native and foreign born. (See "Native" and "Foreign Born" under "Citizenship Status.")

The 2000 decennial census place of birth question matches the 1999 and subsequent American Community Survey (ACS) questions. The 1990 decennial census place of birth question matches the 1996-1998 ACS questions. For the 2000 decennial census and post-1998 ACS samples, separate check boxes and write-in spaces were used for people born in the United Sates and those born outside the United States.

Data on place of birth have been collected in each U.S. census since 1850. In prior censuses, the place of birth question asked respondents to report the state or foreign country where they were born. There were no check boxes in prior censuses. Nonresponse to the place of birth question has been imputed to some degree since 1970. For 1970 through 1990, state of birth was imputed for people born in the United States; people born outside the United States were assigned "born abroad, country not specified" or "born in an outlying area, not specified." In 2000, a specific Island Area (referred to as "outlying areas" in previous censuses) or country of birth was imputed.

Data on place of birth for Puerto Rico was asked beginning in 1910. In censuses prior to 2000, the place of birth question asked respondents to report the municipio in Puerto Rico as well as the U.S. state or the foreign country where they were born. Tabulations for those censuses showed people who were born in the same or a different municipio. Municipio of birth was not asked in 2000. Nonresponse was imputed in 1980 and 1990 for all questions, but a specific foreign country was not imputed until 2000.

Parental nativity (birthplace of parents) was asked of a sample of the population in each decennial census between 1870 and 1970. The 1980, 1990, and 2000 decennial censuses instead included a question on ancestry, except for the U.S. Island Areas (such as Guam) which asked the parental nativity question. (See "Ancestry.")

The census questions on nativity, citizenship status, and year of entry were not designed to measure the degree of permanence of residence in the United States. The phrase "to live" was used to obtain the year in which the person became a resident of the United States. Although the respondent was directed to indicate the year he or she entered the country "to live," it was difficult to be sure that respondents interpreted the phrase as intended.

The year of entry questions for the 2000 decennial census and for the American Community Survey (ACS) are identical. This question differs from the year of entry question in the 1990 decennial census. The 1990 decennial census item asked "When did this person come to the United States to stay?" Moreover, the year of entry question in the 1990 census provided respondents with a fixed number of response categories, while the year of entry question in both the 2000 decennial census and the ACS collect year of entry through a write-in space.

This category includes respondents who indicated that they were born in the United States, Puerto Rico, a U.S. Island Area, or abroad of American parent or parents. People who indicated that they were U.S. citizens through naturalization are also citizens.

This category includes respondents who indicated that they were not U.S. citizens.

The native population includes people born in the United States, Puerto Rico, or the U.S. Island Areas (such as Guam). People who were born in a foreign country but have at least one American (U.S. citizen) parent also are included in this category. The native population includes anyone who was a U.S. citizen at birth.

The foreign-born population includes all people who were not U.S. citizens at birth. Foreign-born people are those who indicated they were either a U.S. citizen by naturalization or they were not a citizen of the United States.

Census 2000 does not ask about immigration status. The population surveyed includes all people who indicated that the United States was their usual place of residence on the census date. The foreign-born population includes: immigrants (legal permanent residents), temporary migrants (e.g., students), humanitarian migrants (e.g., refugees), and unauthorized migrants (people illegally residing in the United States).

The foreign-born population is shown by selected area, country, or region of birth. The places of birth shown in data products were chosen based on the number of respondents who reported that area or country of birth. (See "Place of Birth.")

The citizenship status questions for the 2000 decennial census and the 1990 decennial census are identical.