About the Census

By constitutional mandate, the United States has taken a census of the population every 10 years since 1790. The census provides base-level data on demographic, social, and economic characteristics of persons, households, and housing for a broad range of geographic areas.

In addition to the decennial census, the Census Bureau continuously calculates population and housing estimates and projections and produces special population reports on a wide range of topics. Every 5 years, the economic census surveys business establishments and produces data on business and industry by geographic area and economic sector. The agricultural census (which was transferred to the Department of Agriculture in the 1990s) surveys all sizes and types of farm operations.

Availability of Census Data

Printed census reports, maps, and abstracts have been published since 1790 and are widely available in libraries (including Reed’s) through the Government Printing Office's Federal Depository Library Program. Publication and distribution of census data has evolved rapidly since 1980, when aggregated data from the census was first distributed on machine-readable tapes. Data from the 1990 census were the first to be distributed on CD-ROMs. While some printed reports and DVDs are being published now, the 2000 census was the first to be distributed primarily via the web.

Raw data from census questionnaires presents special problems. By federal law, the Census Bureau must protect the privacy of individuals by closing census records until 72 years after the census is taken (e.g., records from the 1930 census were released in 2002). However, organizations like ICPSR are able to make raw census data available by extracting personal information such as names and addresses from individual census records. In addition, the Census Bureau distributes Public Use Microdata Samples (PUMS). Unlike aggregated data, microdata samples preserve the individual and household relationships at the record level from the original census responses while extracting personal identifying information.

Essential Census Concepts

• 100 percent vs. sample data

100 percent data is collected on the short form questionnaire that is sent to every household (that the Census Bureau could identify) in the U.S. This survey includes number of persons, age, sex, race(s), type of housing, etc. Sample data is collected on the long form questionnaire, which was distributed to a sample of the U.S. population (about one in six households in 2000). Sample data includes variables such as ethnicity, educational attainment and occupation, type and value of home, etc. The forms used in the census are available on the Questionanaires page.

The Census Bureau plans to replace the long form in 2010 with the American Community Survey, an annual survey of social and economic data.

• Geography

Census data is available for a wide range of geographic areas. Areas can be political entities (congressional districts, cities, states, counties) or defined for census purposes (metropolitan statistical areas or census tracts) and are reviewed and revised for each decennial census. Not all variables are available for all geographic areas.

• Data definitions

To understand census data, it’s often necessary to understand precisely how the various terms have been defined. See the Glossary when you need answers about census terminology.

Created by: Dena Hutto, Sociology Liaison & Marc Schneiberg, John C. Pock Professor of Sociology