Source: U.S. Bureau of the Census, Population Estimates Program (PEP). Updated annually. http://www.census.gov/popest/. Census Bureau, 2000 Census of Population, Public Law 94-171 Redistricting Data File. Updated every 10 years. http://factfinder2.census.gov.
Estimates are made for the United States, states, counties, places, and metropolitan areas within the United States. The timing of estimates and availability of demographic detail vary by geographic level. The schedule of releases is available at http://www.census.gov/popest.
The Census Bureau's Population Estimates Program (PEP) produces July 1 estimates for years after the last published decennial census (2000). Existing data series such as births, deaths, and domestic and international immigration, are used to update the decennial census base counts. PEP estimates are used in federal funding allocations, in setting the levels of national surveys, and in monitoring recent demographic changes.
With each new issue of July 1 estimates, PEP revises estimates for years back to the last census. Previously released estimates are superseded. Revisions to estimates for prior years are usually due to input data updates, changes in methodology, or legal boundary changes.
Scope and Methodology:
The population shown for April 1, 2000, is based on Census 2000, revised as necessary to reflect corrections to the census figures or adjustments to account for any boundary changes subsequent to the census.
County population estimates are created by starting with that base population for April 1, 2000. The estimated number of births for the time period since April 1, 2000 is added and the estimated number of deaths for the time period is subtracted. The result is adjusted for net migration, which is calculated using several components including net internal migration, net foreign-born international migration, net movement to/from Puerto Rico, net movement of federal and civilian citizens, the change in group-quarters population, and native emigration from the United States. Birth and death data are obtained through vital statistics, domestic migration is estimated through the address matching of federal tax returns, and international migration data is supplied by the Immigration and Naturalization Service.
County population estimates are produced with this component-of-population-change method, while the state population estimates are solely the sum of the county populations. The following documentation describes the work that is being carried out in the production of the latest published population estimates.