Census Tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity that are updated by local participants prior to each decennial census. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of statistical data. Census tracts generally have a population size between 1,200 and 8,000 people, with an optimum size of 4,000 people. A census tract usually covers a contiguous area; however, the spatial size of census tracts varies widely depending on the density of settlement. Census tract boundaries are delineated with the intention of being maintained over a long time so that statistical comparisons can be made from census to census. Census tracts occasionally are split due to population growth or merged as a result of substantial population decline.
Source of definition: U.S. Census Bureau, Geography Division. Geographic Terms and Concepts – Census Tract
Date of definition: July 2013
Note on changes in census tracts: Changes are made to the boundaries of census tracts with each decennial census.
Note on data presented by census tracts in IECAM: IECAM does not present data by census tracts in its online database. However, IECAM sometimes uses census tract data to make estimates for special purposes.
Web Resources: Geographic Regions
- IPUMS-USA’s “Composition of PUMAs and Super-PUMAs”
2000 PUMAs and on the composition of the 2000 PUMAs by state
- United States Census Bureau: Geographic Terms and Concepts –
- Illinois Department of Human Services: Division of Human Capital Development (HCD)
- United States Census Bureau: 2010 Census Public Use Microdata Area (PUMA) Reference Maps – Illinois
A list of which counties and/or which parts of counties are associated with which PUMAs, and for maps of the 2010 PUMAs for Illinois