Source: U.S. Bureau of the Census, Population Estimates Program (PEP). Updated annually. http://www.census.gov/popest/.
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/schedule.html.
These data are derived from estimates of the resident population of all U.S counties and county equivalents by single years of age (age 0, 1, 2,....85 and over) for July 1 of the reference year, for years since 2010, or for April 1 for 2010.