United States census

The United States census (plural censuses or census) is a decennial census that is legally mandated by the Constitution of the United States. The first census after the American Revolution was taken in 1790 under Secretary of State Thomas Jefferson. There have been 24 federal censuses since that time. The census includes territories of the United States. The United States Census Bureau is responsible for conducting the census.

The most recent national census took place in 2020; the next census is scheduled for 2030. Since 2013, the Census Bureau began discussions on using technology to aid data collection starting with the 2020 census. In 2020, every household received an invitation to complete the census over the Internet, by phone or by paper questionnaire. For years between the decennial censuses, the Census Bureau issues estimates made using surveys and statistical models, in particular, the Population Estimates Program and American Community Survey.

Censuses between 1940 and 2000 (both included) also had a "long form" version, sent to only a subset of the households, with additional questions about socioeconomic and housing characteristics.

The United States census is distinct from the Census of Agriculture, which is no longer the responsibility of the Census Bureau. It is also distinct from local censuses conducted by some states or local jurisdictions.

The U.S. census is mandated by Article I, Section 2 of the United States Constitution, which states: "Representatives and direct Taxes shall be apportioned among the several States... according to their respective Numbers... . The actual Enumeration shall be made within three years after the first meeting of the Congress of the United States, and within every subsequent Term of ten Years". Section 2 of the Fourteenth Amendment amended Article I, Section 2 to include that the "respective Numbers" of the "several States" will be determined by "counting the whole number of persons in each State, excluding Indians not taxed." The United States Census Bureau (officially the Bureau of the Census, as defined in Title 13 U.S.C. § 11) is responsible for the United States census. The Bureau of the Census is part of the United States Department of Commerce.

Title 13 of the United States Code governs how the census is conducted and how its data is handled. Information is confidential as per 13 U.S.C. § 9. The census law, coupled with the Sentencing Reform Act of 1984 (Title 18 of the United States Code, Sections 3551, 3559, and 3571), provides for penalties of up to $5,000 for not responding or for willfully providing false answers to any question.

Decennial U.S. census figures are based on actual counts of persons dwelling in U.S. residential structures. They include citizens, non-citizen legal residents, non-citizen long-term visitors and undocumented immigrants. The Census Bureau bases its decision about whom to count on the concept of usual residence. Usual residence, a principle established by the Census Act of 1790, is defined as the place a person lives and sleeps most of the time. The Census Bureau uses special procedures to ensure that those without conventional housing are counted. Data from these operations are not as accurate as data obtained from traditional procedures.

In instances where the bureau is unsure of the number of residents at an address after a field visit, its population characteristics are inferred from its nearest similar neighbor (hot-deck imputation). This practice has effects across many areas, but is seen by some as controversial. The practice was ruled constitutional by the U.S. Supreme Court in Utah v. Evans.