Getting Started with Census Data

New to census data? It's a complex subject, but the Missouri Census Data Center can help you find what you need.

Census data is a general term encompassing official data products released by the U.S. Census Bureau as well as secondary data derived from those products by additional filtering, analyzing, or combining. Most MCDC data applications work with this secondary census data.

Deciding which census data product or application to use is often the most difficult part of the process. A beginning data user should consider several questions to help identify the best data source:

Subject / Detail

Are you looking for "typical" broad census subjects, such as population totals, families, age, sex, or race? If so, the standard decennial census (what most people think of when they hear the word "census") will provide the most accurate information for any geographic area. Or, are you interested in finer details, such as income, immigration, housing, employment, and so on? The American Community Survey (ACS) includes many detailed subjects that aren't on the main census.

If all you're looking for is simple population data, the MCDC population estimate applications may be best. These secondary data sets are compilations of primary source data, and cover more years and geographic areas than standard census products.


What type of area are you interested in — state, county, township, city, town, metro area, zip code, tract, or something else? Most census data sets cover the larger areas like states and counties, but coverage of smaller areas varies by the application or product.

The decennial census provides data for all geographic levels down to block groups. For the ACS, however, whether a geographic area is included depends on its population. Small areas (under 20,000 population), like towns, unincorporated places, tracts, or block groups, are available only in the ACS 5-year data sets. Larger areas, such as small cities, rural counties, and urban school districts, are generally available in the ACS 3-year and 5-year data sets. And the largest areas (over 65,000 population), including all states, urban counties, larger cities, metro areas, etc., are available in the ACS 1-year, 3-year, and 5-year datasets. For more information, refer to the American Community Survey page.

Time Period

How important is it to get the latest data available? Would you trade timeliness for statistical accuracy?

As its name indicates, the decennial census happens only once every ten years, so even the most recent data can be as "stale" as ten years old. However, because the decennial census counts every U.S. resident ("100-percent data"), it's the most statistically accurate data available for the subjects it covers.

ACS data is released every year, making it among the most recent data available. But, each ACS data release represents only a sample of the population, which means that it's subject to various kinds of statistical error. This is especially true at smaller geographic areas, where, due to sample size, many data points are essentially unusable.