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What is the Decennial Census?
What is the Decennial Census?
A census is a complete count of a population, generally a nation, conducted by government, as of a fixed date."
International Encyclopedia of the Social & Behavioral Sciences (2nd Edition), 2015, Page 302
The United States Constitution (Article 1, Section 2) mandates a decennial census for the purpose of Congressional apportionment. The first Census was conducted 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, and ethnicity as well as a variety of social and economic characteristics. While there are undoubtedly portions of the population that go uncounted, it is the closest we have to complete demographic and economic data on the U.S. population.
Census Questions & Variables
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 at the Library.
Between 1970 and 2000 the Decennial Census included a “short form” with questions answered by every household in the country (a census), as well as a “long form” that is answered by about 1 in 6 households (a sample). The Census Bureau began using sampling in 1940 and experimented with various methods in the 1940, 1950, and 1960 Censuses. 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, housing, etc.) are the basis for the Census sample data (available in summary file 3 & 4). The 2010 Census did not include a long form; instead, sample data previously collected on the long form is now collected regularly through the American Community Survey (ACS).
Starting Points for Census Statistics
- Social Explorer This link opens in a new window1790-2010+. Data from the decennial Census and the American Community Survey, with a user-friendly interface. Allows the creation of maps & statistical tables. Census Tract boundaries are available back to 1940. Also includes religion surveys from 1980-2010, which are not affiliated with the U.S. Census.
- data.census.govHosted by the Census Bureau, the statstics provided at data.census.gov come from several censuses and surveys about the United States, Puerto Rico and the Island Areas (territories).
- National Historic GIS (NHGIS)Provides, free of charge, aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2015. Hosted by the Minnesota Population Center.
Other Censuses
- Census of AgricultureCollects data on number and size of farms and ranches, costs of production, value of products and selected characteristics of the owners. (Use NUSearch to identify related print publications.)
- Economic CensusCollects data on size and number of business establishments, number of employees, sales, shipments, receipts, payroll, and whether women or minority owned. (Use NUSearch to identify related print publications.)
- Census of GovernmentsCollects data on state and local governments. Data collected includes number and types of governments, number of employees and payroll, budgets and revenues, and fiscal relationships between governments. (Use NUSearch to locate related print publications.)
- Census Survey ExplorerThis tool helps you identify relevant datasets among the more than 120 surveys conducted by the Census Bureau each year. Search by keyword, then filter by geography, frequency, topics, and subtopics to identify the best dataset to answer your questions.
2020 Census Data Releases
2016-2020 American Community Survey (ACS) 5-year estimates now available
- Released March 17, 2022, the 2016-2020 American Community Survey (ACS) five-year estimates, featuring more than 40 social, economic, housing and demographic topics such as home ownership rates and costs, health insurance coverage and educational attainment are now available at data.census.gov.
Estimates of Undercount and Overcount in the 2020 Census (March 10, 2022)
- The Post-Enumeration Survey (PES) and Demographic Analysis Estimates (DA) estimate how well the 2020 Census counted everyone in the nation and in certain demographic groups. They estimate the size of the U.S. population and then compare those estimates to the census counts.
2020 Census Redistricting Results, via data.census.gov
- Easier-to-use format
- identical data to the August 12, 2021 release
- Guidance for 2020 Redistricting Data Users
2020 Census Redistricting Results, Release August 12, 2021
- The August 12, 2021 release will be in Summary File format and accessible on the Census Bureau's public FTP site.
- The same data in easier-to-use formats will be made available by September 30, 2021 at data.census.gov
- 2020 Census Redistricting Data FAQ
- Disclosure Avoidance Modernization
- 2020 Census Demographic Data Map Viewer (forthcoming)
2020 Census Redistricting Data hosted at NHGIS
- The National Historic GIS repository also provides 2020 GIS boundary files, geographic crosswalks between 2010 and 2020 census blocks, and demonstration data to assess 2020 data quality due to changes in privacy protections implemented by the Census Bureau.
2020 Census Redistricting Data by State - CISER @ Cornell
- On August 12, 2021, the Census Bureau released Public Law 94-171 data, or Redistricting data, in four parts per state. CISER @ Cornell has integrated these and made them available in convenient ready-to-use formats -- SAS, SPSS, STATA, and CSV. CISER also provided program files in SAS, SPSS, and Stata to read the CSVs.
2020 Census Apportionment Results, Released April 26, 2021
A Preliminary Analysis of U.S. and State Level Results From The 2020 Census
- 2020 Census Redistricting Data @ NHGIS2020 Redistricting Data is accompanied by 2020 GIS boundary files, geographic crosswalks between 2010 and 2020 census blocks, and demonstration data to assess 2020 data quality due to changes in privacy protections implemented by the Census Bureau.