Decennial census

The decennial census is the U.S. Census Bureau's population and housing census conducted every ten years. “Decennial” means occurring once a decade. It provides a population count tied to a specified reference date, rather than a continuously updated count of everyone currently living in a community.

The date is part of the count

The Census Bureau conducts the decennial census in years ending in zero, with April 1 as Census Day. The counts are used for purposes including allocating seats in the U.S. House of Representatives among the states. Census Bureau overview.

For a community profile, the practical point is the time reference. A count from the 2020 Census remains a 2020 Census count when it appears on a webpage in a later year. The date the page was refreshed does not change the period represented by that number.

Example

Hypothetical: A city profile lists 25,000 residents from a decennial census. A later annual population estimate is 27,000. A public-safety report contains 270 incidents for that later year.

Using 25,000 as the denominator gives 1,080 incidents per 100,000 residents. Using 27,000 gives 1,000. The incident count is the same, but the population source changes the rate. The report should identify its denominator and explain why it fits the period and area being measured.

Common confusion

The decennial census and the American Community Survey are different Census Bureau programs. An ACS estimate describing a five-year period should not be called a new decennial census count.

A census count also differs from a projection of future population. Population estimates and projections use their own methods and dates. “Latest population” can mean several different things unless the source and reference year are stated.

Counts are not a complete explanation of service demand. Residents, daytime visitors, commuters, and people traveling through an area can affect the activity an agency encounters. A resident count describes one population base, not every person present throughout the day.

Reading a census-based profile

Check the census year, geographic area, and whether the figure is a total population count or a narrower group. If boundaries changed after the census, a present-day city outline may not match the area represented by the historical figure.

Keep the original source label when quoting the number. That lets readers distinguish the foundational census count from later estimates and avoids presenting an older measurement as a real-time population total.

Related terms

• American Community Survey
• Population estimate
• Resident population
• Population denominator

Sources

• U.S. Census Bureau: About the Decennial Census of Population and Housing — Establishes the ten-year cycle, April 1 reference date, and apportionment purpose. Rate calculations here are hypothetical.