Source: U.S. Census Bureau, 2010 Census of Population and Housing, updated every 10 years. Decennial Census Datasets
In Census 2010, people were counted at their "usual residence," a principle followed in each census since 1790. Usual residence has been defined as the place where the person lives and sleeps most of the time. This place is not necessarily the same as the person's voting residence or legal residence.
Noncitizens who are living in the United States are included, regardless of their immigration status.
Persons temporarily away from their usual residence, such as on vacation or on a business trip on Census Day, were counted at their usual residence. People who live at more than one residence during the week, month, or year were counted at the place where they live most of the year. People without a usual residence, however, were counted where they were staying on Census Day.
Scope and Methodology:
Place of residence was derived from answers to questions that were asked of all people in Census 2010.
The "April 1, 2010 estimates base" reflects corrections to the Census 2010 figures, where necessary, or adjustments to account for any boundary changes subsequent to the census.
For more information please read the 2010 Census Redistricting Data (Public Law 94-171) Summary File Technical documentation.