Source: U.S. Bureau of the Census, Population Estimates Program (PEP). Updated annually. http://www.census.gov/popest/estimates.php
Estimates are made for the United States, areas within the United States, and Puerto Rico. The frequency of estimates and availability of demographic detail vary by geographic level. The schedule of releases are available at http://www.census.gov/popest/topics/.
Definition:
The Census Bureau''''s Population Estimates Program (PEP) produces July 1 estimates for years after the last published decennial census (2000), as well as for past decades. 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. A methodology reference accompanies most of our population estimates offerings.
In Census 2000, 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.
The U.S. Census Bureau produces estimates of total resident population for each state and county on an annual basis.
Scope and Methodology:
County population estimates are created by starting with the base populations from either Census 2000 or the revised population estimate for the most recent year and then adding or subtracting the demographic components of population change calculated for the time period. The estimated number of births 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.
With each new issue of July 1 estimates, PEP revises estimates for years back to the last census. Previously released estimates become superseded. Revisions to estimates are usually due to input data updates, changes in methodology, or legal boundary changes.
Percent change, April 1, 2000 to [the date of the latest estimate] is calculated by dividing the difference between the latest estimate and the Census 2000 population by the Census 2000 population.
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