The first census in 1790 counted about 3.9 million people. The 2020 census counted 331.4 million. The count is conducted by the Census Bureau, part of the Commerce Department, which also runs dozens of surveys between censuses, including the American Community Survey. Because the census determines political power and money, how it is conducted is fiercely contested.
This guide explains how the census works, what it is used for, and the debates around it.
The House has had 435 seats since 1913, and since 1941 they have been divided among the states using the method of equal proportions. Because each state's electoral votes equal its House seats plus two senators, the census also shifts presidential electoral votes. After the 2020 census, Texas gained two seats and five states gained one, while seven states lost one. Projections suggest continued shifts toward the South and West in 2030.
States receive detailed block-level counts to redraw congressional, legislative, and local districts under one person, one vote. Census data also drive formulas for federal programs such as Medicaid, highway funds, nutrition assistance, and Title I school grants. One study estimated that census-derived data guided about 2.8 trillion dollars in federal spending in fiscal 2021. Businesses, researchers, and local governments use census data for planning.
Supporters of excluding unauthorized immigrants or asking about citizenship argue that apportionment should reflect citizens or lawful residents and that accurate citizenship data serve legitimate purposes. Opponents argue that the Constitution requires counting all persons and that citizenship questions depress responses and worsen undercounts. Preparation for 2030 includes field tests, new technology for online responses, and debates over funding and staffing for an operation that hires hundreds of thousands of temporary workers.
Article I requires an actual enumeration within three years of the first Congress and every ten years after, to apportion House seats and direct taxes. The original Constitution counted enslaved people as three-fifths of a person, and the 14th Amendment replaced that rule with a count of the whole number of persons in each state. Census Day is April 1, and the Census Bureau must deliver state population totals to the President by December 31 of the census year.
Title 13 of the U.S. Code makes individual responses confidential, bars their use against respondents, and allows release only after 72 years. The bureau applies statistical techniques to published data to prevent identification of individuals, an approach that drew criticism from some data users after 2020. A post-enumeration survey found that the 2020 census undercounted Black, Hispanic, and Native American residents on reservations and overcounted some other groups, and that six states were undercounted and eight overcounted.
The census counts all residents, including noncitizens, a practice tied to the 14th Amendment's whole number of persons language. In Department of Commerce v. New York in 2019, the Supreme Court blocked a citizenship question from the 2020 census because the government's stated reason appeared contrived. A 2020 plan to exclude unauthorized immigrants from apportionment counts was not carried out before the administration ended. In August 2025 the President directed the Commerce Department to begin work on a new census excluding people in the country unlawfully, and in 2026 the bureau proposed a citizenship question in a field test for the 2030 census.
See how the count shapes districts in redistricting and gerrymandering explained, follow the money in how federal money reaches your town, or explore other federal data in where government statistics come from.