What is the Decennial Census?
A Decennial Census, for the purpose of Congressional reapportionment is mandated by the U.S. Constitution. The first Census was held in 1790, and counted only heads of household. Over time, the Census has expanded to count every person in the U.S., including information on their age, race, ethnicity and more. While there may be portions of the population that go uncounted, it is still the closest we have to complete demographic and economic data on the U.S. population. Use the tabs or the links below to navigate through this guide.
- Census by Decade
- Census Geography
- Census Compilations
- Guides and Documentation
- Raw Data Sources
- Defining Your Community for Census Research
Census Questions & Variables
Questions change from Census to Census (sometimes dramatically) which means that the statistics available change from decade to decade. The easiest way to find out what information is available for a specific Census is to look at the Census questionnaires. If the question wasn’t asked, the information isn’t available. It’s that simple. For copies of the original Census Questionnaires since 1790, see the Census publication Measuring America: The Decennial Censuses from 1790 to 2000. It is also available in print GovPub Reference C 3.2:M 46/2/REV. and GovPub U.S. Stacks C 3.2:M 46/2 if you prefer.
You can also check out the various years on the "Census by Decade" tab to find the different variables for each year.
For most of the twentieth century the Decennial Census has included a “short form” with questions answered by every household in the country, as well as a “long form” that is answered by about 1 in 6 households. Questions on the short form (age, race, etc.) are the basis for the Census 100% data (available in Summary file 1 & 2). Questions on the long form (education, income, etc.) are the basis for the Census sample data (available in summary file 3 & 4).