University of Illinois Urbana‑Champaign

Geographic Region: Congressional Districts

Congressional districts are the 435 areas from which people are elected to the U.S. House of Representatives. After the apportionment of congressional seats among the states based on decennial census population counts, each state with multiple seats is responsible for establishing congressional districts for the purpose of electing representatives. Each congressional district is to be as equal in population to all other congressional districts in each state as practicable.

All site-based data (e.g., child care) and all demographic data (e.g., population) are available by congressional district on the IECAM database. Non-site-based data (e.g., early intervention, home visiting) are not presented by congressional district.

After each decennial census conducted by the U.S. Census Bureau, the congressional districts for each state are redrawn. The new districts are the basis for the next general election, and they take effect in the Congress after that election. (For example, the latest decennial census was conducted in 2020. The new districts were redrawn in 2021, and they were used as the basis for the general election in November 2022. They took effect with the beginning of the next Congress in January 2023.)

After the 2020 Census, Illinois was apportioned 17 congressional districts, a loss of one district.

Source of definition: U.S. Census Bureau, Geography Division

Comparing congressional districts across decennial censuses

In IECAM’s online database and multiyear search feature, the congressional districts drawn after the 2010 census will be considered one region type and the districts based on the 2020 census will be considered yet another region. Data available for the 18 districts based on the 2010 census include demographic data for years 2011 through 2021 and service data for years 2011 through 2022. Data available for the 17 districts based on the 2020 census begins with 2022 demographic data and 2021 site-based service data.

Because these region types have different numbers of districts (18 for the post-2010 census, 17 for the post-2020 census) and because the districts cover different geographic areas, it is not possible to compare data for post-2010 and post-2020 census districts.

However, you are able to compare data for different years that apply to the post-2010 and post-2020 census districts. For example, you can compare data on PFA capacity or population of children for Congressional District 15 in 2012 and in 2013, and you can compare the same data for Congressional District 15 in 2022 and in 2023 when those data become available.

Below find the two most recent congressional district maps for Illinois. The districts change boundaries only after each decennial Census (every 10 years).

  • Post-2020 Census districts (2023–2032)
  • Post-2010 Census districts (2013–2022)

Post-2020 Census districts

Post-2010 Census districts