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Introduction to U.S. Census Data

Other Censuses & Surveys

The U.S. Census conducts three censuses -- the decennial census, and twice per decade the Economic Census and Census of Governments -- as well as 130 different surveys, including the American Community Survey. Other surveys that may be of interest include:

What is the Decennial Census?

Every 10 years, the U.S. Census Bureau conducts a constitutionally mandated count of the U.S. population through the Decennial Census of Population and Housing. The first Census was conducted in 1790 and counted only heads of household. Over the years, additional questions were added to the decennial census questionnaire to collect information on race, ethnicity, migration, immigration, housing, health, education, and other factors. Changes in Census questionnaires were a reflection of broader societal changes.

In 1940, the long form decennial census questionnaire was introduced to gather more detailed information about households from a sampling of the population. Up through the 2000 decennial census, most households received a short-form questionnaire asking a minimum number of questions designed to collect basic demographic and housing information (e.g., age, race, sex, etc.) to be used for making decisions about the distribution of Congressional seats to states and redistricting. The long form, sent to one-sixth of all households, collected social, housing, and economic information (e.g., citizenship, educational attainment, disability status, employment status, income, and housing costs) that was used to determine the distribution of federal funds for things like transportation, education, neighborhood improvements, public health, and so on.

In 2005, the U.S. Census Bureau launched the American Community Survey (ACS), a nationwide survey designed to provide communities with reliable and timely social, economic, housing, and demographic data every year. It is sent to a small percentage of the population on a rotating basis. In 2010, the ACS replaced the long form questionnaire, allowing the 2010 and 2020 Censuses to be a short form only. You can learn more about the history of the U.S. Census here.

Excerpts from U.S. Census Bureau

Decennial Census vs. American Community Survey

There are several censuses and many surveys but the two most commonly used are the decennial census and the American Community Survey (ACS). The table below highlights important differences between the two and should aid you in deciding which to use for your research.

Should you use the decennial census or ACS?  Ask yourself these questions:

  • What population characteristics am I interested in? 
    • If you only want the most general population counts and characteristics (age, sex, race), your best bet is the decennial census (or official Population Estimates for county geographies and larger for intercensal years -- i.e., the intervening years between censuses). 
    • If you want more descriptive population characteristics (e.g., education, income, nativity), you have to work with the ACS. 


  • What type of geography am I interested in? 
    • If you are interested in larger geographies (states, larger cities/metropolitan statistical areas, or populous counties), the ACS 1-year is a good choice. 
    • If you are interested in smaller geographies (census tracts, rural areas), you will have to choose the ACS 5-year estimates.