The Population Estimates Program (PEP) at the U.S. Census Bureau produces yearly estimates after each published decennial census (the last one being in 2000). Existing data on births, deaths, Federal tax returns, medicare enrollment, and immigration, are used to update the decennial census base counts.
PEP prepares estimates of the population by age, sex, race, and Hispanic origin for the nation, states and counties. It also prepares estimates of the total population of functioning governmental units, and estimates of the number of housing units for states and counties. The estimates developed from this program are used for a variety of purposes including the annual allocation of over $200 billion in federal funds, as denominators for statistical indicators, and the basis for program planning and development.