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Census Basics

summary of important basic information on finding and using Census data

Population Surveys: Quick Links

More about Population Surveys

Decennial Census (latest is 2010)

chartThe most comprehensive Census survey is the Decennial Census, which counts everyone in the U.S. It happens every ten years (in years ending in 0). Basic data on the population (age, sex, race) is available by the beginning of the next year (i.e., 2011, 2021, etc.). More detailed information is released later, sometimes up to 3 years after the Census is taken.

American Community Survey (ACS)

peopleThis survey is taken continually, as a way to update information in between Decennial Censuses. However, this is a true survey, and not a complete count. It is taken by asking questions of samples of the population. (For more information on the ACS, see this box.)

In Census tables you will see 1-year, 3-year and 5-year ACS estimates. Here is a summary of what these distinctions mean:

  • 1-year estimates. Include 12 months of collected data for places with populations over 65,000, released every year. It is obviously the most current data, but it's also the least reliable, since it uses the smallest sample size.
  • 3-year estimates (will be discontinued). Include 36 months of collected data for places with populations over 20,000, released every three years.
  • 5-year estimates. Include 60 months of collected data for all places, released every five years. Less current, but more reliable, due to the larger sample size.

Can you compare data from different surveys?


Yes, in some cases. Below is a link to a summary of what should and should not be compared. The page includes links to a tool that will give you precise tables to compare.

Other Census Surveys

gearsThe Census Bureau also conducts surveys of economic and governmental activity. These Censuses are conducted every five years. Here are portals to this data:

(For more information and links, see the appropriate tabs in this Research Guide.)

Historical Census Data

noteSome historical data is available online and more is being digitized all the time. Here are some important links to historical Census data:

(For more information and links, see this Research Guide. For information on historical Census publications in the Library, see this Guide.)