University of Illinois Urbana‑Champaign

Geographic Region: Census Tracts

Census tracts are small subdivisions of a county and generally have a population size between 1,200 and 8,000 people. In some instances, census tracts can be used to explore data trends and patterns on a neighborhood scale across the state.

About the data

Census tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity that are updated by local participants before 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 because of 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

IECAM does not present data by census tracts in its online database. However, IECAM sometimes uses census tract data to make maps/charts or estimates for special purposes.