The official U.S. Census is described in Article I, Section 2 of the Constitution of the United States. It calls for an actual enumeration of the people every ten years, to be used for apportionment of seats in the House of Representatives among the states. The first official Census was conducted in 1790 under Thomas Jefferson, who was the Secretary of State. That census, taken by U.S. marshals on horseback, counted 3.9 million inhabitants. Since that time, the decennial Census has been conducted every ten years, generally on April 1 in years ending in a zero.
Besides providing the basis for congressional redistricting, Census data are used in many other ways. Since 1975, the Census Bureau has had responsibility to produce small-area population data needed to redraw state legislative and congressional districts. Other important uses of Census data include the distribution of funds for government programs such as Medicaid; planning the right locations for schools, roads, and other public facilities; helping real estate agents and potential residents learn about a neighborhood; and identifying trends over time that can help predict future needs. Most Census data are available for many levels of geography, including states, counties, cities and towns, ZIP Code Tabulation Areas, census tracts, blocks, and much more.
The 2010 Census represented the most massive participation movement ever witnessed in our country. Approximately 74 percent of the households returned their census forms by mail; the remaining households were counted by census workers walking neighborhoods throughout the United States. National and state population totals from the 2010 Census were released on December 21, 2010. Redistricting data, which include additional state, county and local counts, was released starting in February 2011.
For the 2000 Census, additional questions were asked of a sample of persons and housing units (generally 1 in 6 households) on topics such as income, education, place of birth and more. Information on those topics are now available as part of the American Community Survey.
For the 2010 Census, 10 questions were asked of every person and housing unit in the United States. Information is available on:
The results from the 2010 Census are available in a number of datasets in American FactFinder:
Other decennial data sets: