Every ten years, the United States tries to count every single person living in the country. It is the largest peacetime operation the federal government runs, and its results decide how many seats each state gets in Congress, how electoral districts are drawn, and how trillions of dollars in federal funding are shared out. Yet most Americans only meet the census once a decade, when a form arrives in the post, and many are unsure what it is for, what it asks, or what happens to their answers. This guide explains what the US census is, how it works, what it decides, and what to expect from the next one in 2030. All figures come from the US Census Bureau and the sources checked today.
A count required by the Constitution
The census is not a policy choice. It is written into the Constitution. Article I, Section 2 requires an “actual Enumeration” of the population within every ten-year period, and the count has run without interruption since the first one in 1790. The 2020 census was the 24th count in American history, and the next one, in 2030, will be the 25th. The US Census Bureau, part of the Department of Commerce, runs the operation.
The purpose is straightforward: count everyone, once, in the right place. The count covers all 50 states, the District of Columbia and the five US territories: Puerto Rico, the US Virgin Islands, Guam, American Samoa and the Commonwealth of the Northern Mariana Islands. Everyone is counted where they usually live on Census Day, 1 April of the census year, regardless of citizenship or immigration status. That matters: the census is a count of residents, not a count of citizens or voters. Students are counted where they live while studying, not at their parents’ address, and the same usual-residence rule applies to everyone else.
How the count actually works
In the weeks before Census Day, households receive invitations to respond online, by phone or by post. The form asks basic demographic questions: how many people live at the address, and their age, sex and race. The Census Bureau must tell Congress which subjects the census will cover at least three years ahead, and the exact wording of the questions at least two years ahead, so there are no surprises.
If a household does not respond, the Bureau follows up. Census takers visit homes in person to collect the information, and the Bureau also uses administrative records to fill gaps. The law sets hard deadlines: under Title 13 of the US Code, the Bureau must deliver state population totals to the President by 31 December of the census year, and detailed redistricting data to each state by 1 April of the following year, so state legislatures can redraw district lines. The 2020 apportionment results were delivered on 26 April 2021.
Your answers are protected by law. Title 13 makes census responses confidential and requires that they be used for statistical purposes only. The Bureau cannot share individual responses with other government agencies, law enforcement or the courts, and census workers take an oath to protect confidentiality for life.
What the census decides: seats in Congress
The census has one constitutional job above all others: apportionment. That is the process of dividing the 435 seats in the US House of Representatives among the 50 states according to population, using a formula called the method of equal proportions. The District of Columbia and Puerto Rico are not included in apportionment because they do not have voting seats in Congress.
The 2020 census moved seven seats among 13 states. Texas gained two seats, and Colorado, Florida, Montana, North Carolina and Oregon each gained one. California, Illinois, Michigan, New York, Ohio, Pennsylvania and West Virginia each lost one seat, and the remaining 37 states saw no change. It was the smallest number of seats shifting between states in any census, according to the Bureau’s own account. The states with the most representatives after 2020 are California with 52 seats and Texas with 38.
The numbers behind those shifts are large. The resident population counted on 1 April 2020 was 331,449,281, an increase of 7.4 percent since the 2010 census counted 308,745,538 people. The apportionment population, which adds Americans living overseas who can be allocated to a home state, was 331,108,434. California was the most populous state, with 39,538,223 residents, and Wyoming the smallest, with 576,851. After the first census in 1790, each member of the House represented about 34,000 residents; after 2020, each member represents an average of 761,169 people. Because each state’s Electoral College votes equal its House seats plus its two senators, the census also reshapes presidential elections: our guide to what the Electoral College is explains how.
What the census decides: money for communities
The census also shapes where federal money goes. The Census Bureau’s own estimate, published in 2023, found that 353 federal assistance listings used decennial census programmes data, in whole or in part, to distribute more than $2.8 trillion in fiscal year 2021 to states, communities, tribal governments and other recipients. That broad category includes the decennial census, the American Community Survey, geographic programmes and related population estimates, and it is a historical figure for one year, not a current total. A separate analysis by the Project On Government Oversight found that 371 federal programmes directed more than $2.24 trillion in census-guided funding in fiscal year 2023.
It is important to be precise about what that means. The Census Bureau itself does not distribute any federal funds, and it does not decide how much any programme gets. Federal programmes use census data in their own formulas: to define who is eligible, to allocate money between places, or to rank applications. Programmes informed by census results include Medicaid, Head Start, community mental-health block grants and the Supplemental Nutrition Assistance Program. A community that is undercounted can therefore receive less than its fair share for a full decade, because the census only happens once every ten years and its results are the baseline for the surveys and estimates that follow.
The census between censuses
The ten-year gap does not mean the Bureau goes quiet. Between censuses, it runs the American Community Survey, which collects detailed social, economic and housing information every year, and the Population Estimates Program, which produces annual estimates of population and housing units for states, counties, cities and towns. Both use the decennial census as their baseline, which is why an accurate count matters for the whole decade, not just for the year it happens. The Bureau also publishes the data openly: anyone can explore census results on its data platform, data.census.gov.
Looking ahead: the 2030 census
The next census is already being planned. Census Day for the 2030 census is 1 April 2030. Planning began in 2019, and the Bureau is now in its development and integration phase, which includes a limited census test in 2026 at two test-site locations. Notifications will arrive in mailboxes in March 2030, ahead of Census Day. The apportionment results from the 2030 count will determine House seats and Electoral College votes from roughly 2033 through the following decade.
One thing to watch: in September 2026 the Census Bureau proposed a change to the 2030 census that would leave out some noncitizens when calculating how many seats each state gets in the House. The proposal was still under discussion at the time of writing, and it could be challenged in court, so check census.gov for the latest position before the count begins. What is not in doubt is the date: 1 April 2030, and every person living in the United States on that day is meant to be counted.
Common questions
Do I have to answer the census? Yes. Responding to the census is required by law, and the Bureau follows up with households that do not respond. The form is short, and it asks only basic facts about who lives at the address.
Will my answers be shared with other agencies? No. Title 13 of the US Code protects the confidentiality of your responses, and they can be used for statistical purposes only. The Bureau cannot share individual answers with immigration authorities, law enforcement or any other agency.
Does the census ask about citizenship? The 2020 census did not ask about citizenship. It asked how many people lived at the address and basic demographic facts such as age, sex and race. The questions for 2030 must be finalised and reported to Congress at least two years ahead, so the exact list will be public well before Census Day.
Can the census be done online? Yes. In 2020, households could respond online, by phone or by post, and the Bureau expects the same options in 2030. If you do not respond, a census taker may visit in person.
Why does it matter if my town is undercounted? Because the count sets representation and funding for ten years. Fewer people counted can mean fewer dollars for schools, roads, hospitals and food programmes, and in close cases it can cost a state a seat in Congress.
The bottom line
The census is simple to describe and enormous to run: every person, counted once, in the place they usually live, every ten years. The 2020 count found 331,449,281 residents, moved seven House seats among 13 states, and set the baseline for trillions of dollars in federal funding. The next count is on 1 April 2030, and it will be the 25th in American history. When the invitation arrives in March 2030, answer it: it takes minutes, your answers are confidential by law, and the results will shape your community’s representation and funding until 2040. For how those seats shape presidential elections, see our guide to what the Electoral College is, and for the court that has ruled on census disputes, our guide to how Supreme Court rulings work.
Sources verified 14 Nov 2026: US Census Bureau — 2020 Census Apportionment Results — resident population 331,449,281 as of 1 April 2020, up 7.4 percent from 308,745,538 in 2010; apportionment population 331,108,434; seven seats shifting among 13 states, Texas plus two, Colorado, Florida, Montana, North Carolina and Oregon plus one each, California, Illinois, Michigan, New York, Ohio, Pennsylvania and West Virginia minus one each; California largest at 39,538,223, Wyoming smallest at 576,851; average House district 761,169 people; about 34,000 residents per member after 1790; results delivered 26 April 2021; Project On Government Oversight — Census Matters — 371 federal programmes directed more than $2.24 trillion in census-guided funding in fiscal year 2023; constitutional basis and process (Article I, Section 2, actual Enumeration every ten years; first census 1790; 2020 the 24th count; 2030 the 25th; Census Day 1 April 2030; notifications March 2030; planning from 2019; 2026 census test at two sites; Bureau to deliver state totals to the President by 31 December of the census year and redistricting data by 1 April the following year; Title 13 confidentiality; 435 House seats; method of equal proportions; five territories counted) and funding figures (Census Bureau fiscal year 2021 estimate: 353 assistance listings, more than $2.8 trillion; Bureau distributes no funds itself; Medicaid, Head Start, mental-health block grants and SNAP among programmes informed by census data; September 2026 proposal on noncitizens in apportionment) as confirmed in checked sources today. No figure was taken from memory.