About the Decennial Census

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 codes, census tracts and blocks, and much more.

Taking the decennial census is a big project. For Census 2000, many people were hired to assist in counting the population; temporary employment peaked at about 475,000 one week. New homes are constantly being built, and older homes are torn down. Some people don't like to provide the government with information about themselves. Sometimes the census forms are lost, or people forget to fill them out. However, each census in modern times has improved in its accuracy. For the 2000 census, the Census Bureau employed more than 500,000 people to visit the homes of people who did not return their mail-in census form. The 2000 census turned out to be the most accurate in history, with the lowest undercount of minorities of any previous census.

What's asked - the Short Form and the Long Form

100-percent characteristics (short form): A limited number of questions were asked of every person and housing unit in the United States. Information is available on:

Sample characteristics (long form): Additional questions were asked of a sample of persons and housing units (generally 1 in 6 households). Data are provided on: