University of Illinois Urbana‑Champaign

Geographic Regions: State House and Senate Districts

About the data

The legislative power of the state is vested in the General Assembly, which is composed of a 59-member Senate and a 118-member House of Representatives. Its principal activities are enacting, amending, or repealing laws; passing resolutions; adopting appropriation bills; and conducting inquiries on proposed legislation. Each legislative district is composed of one Senate district, which is divided into two Representative districts. Every two years, one Representative is elected from each Representative district for a two-year term. Members of the General Assembly are elected in the general election in even-numbered years. Senate districts are divided into three groups, and one or two groups are elected every two years.

Each General Assembly consists of two sessions, one in each year after the general election.

The U.S. Census Bureau first reported data for state legislative districts (SLDs) as part of the 2000 Public Law (P.L.) 94-171 Redistricting Data File. The SLDs embody the upper (Senate) and lower (House) chambers of the General Assembly.

Source of definition:

For information on current state House and Senate members, consult the Illinois Blue Book. Illinois House/Senate map data source: Illinois State Board of Elections.

Notes

After each decennial census conducted by the U.S. Census Bureau, the House and Senate districts are redrawn. The new districts are the basis for the next general election, and the new districts take effect in the general assembly after that election.

Thus, after the 2010 Census, the state House and Senate districts were redrawn in 2011. These districts will be used as the basis for the general election held in November 2012. They took effect with the beginning of the subsequent General Assembly in January 2013.

Post-Census 2020 legislative districts

The Illinois legislature passed a congressional plan (HB 1291) on Nov. 11, 2021. The Governor signed the bill on Nov. 23, 2021.

"The Illinois legislature used American Community Survey (ACS) data and passed a state legislative plan (HB 2777) on May 28, 2021, which the Governor signed on June 4, 2021. Following the release of the 2020 Census data on Aug. 12, 2021, the state legislature passed a second redistricting plan (SB 297), which the Governor signed on Sept. 24, 2021.

The state redistricting plans were challenged in federal court (See McConchie v. Ill. State Board of ElectionsContreras v. Ill. State Board of Elections and UCCRO v. Ill. State Board of Elections). The initial plan (HB 2777) using ACS data was ruled unconstitutional on Oct. 19, 2021. The second plan (SB 297) was upheld on Dec. 30, 2021." Source: Loyola Law School Redistricting website

The Census 2020 districts are in effect from: 103rd General Assembly, Session One, 2023 through: 107th General Assembly, Session Two, 2032. 

IECAM will report data by Census 2020 Illinois State House and Senate districts for most site-based services and most demographic variables from FY2023 (school year 2022-2023) through FY2032 (school year 2031–2032). In addition, IECAM will report data for some site-based services according to these districts for 2021 and 2022 (years when those districts were not actually in effect) to provide a baseline comparison for later data.

Post-Census 2010 legislative districts

The Census 2010 districts are in effect from: 98th General Assembly, Session One, 2013 through: 102nd General Assembly, Session Two, 2022

IECAM will report data by Census 2010 Illinois State House and Senate districts for most site-based services and most demographic variables from FY2013 (school year 2012-2013) through FY2022 (school year 2021–2022). In addition, IECAM will report data for some site-based services according to these districts for 2011 and 2012 (years when those districts were not actually in effect) to provide a baseline comparison for later data.

Post-Census 2000 legislative districts

The Census 2000 districts were in effect from: 93rd General Assembly, Session One, 2003 through: 97th General Assembly, Session Two, 2012

Note on census 2000 districts reported in IECAM: IECAM began reporting data by Census 2000 Illinois State House and Senate districts for some site-based services and most demographic variables beginning with FY2006 (school year 2005–2006). Reporting by Census 2000 districts continued through FY2012 (school year 2011–2012)

Data available on IECAM

Almost all site-based data (e.g., child care) and almost all demographic data (e.g., population) are presented by state House and Senate district in IECAM. Non-site-based data (e.g., early intervention) are not presented by state House and Senate district.

Note on comparing legislative districts across decennial censuses: In IECAM’s online database and in the multiyear search feature, the legislative districts up through 2022 (the last year of districts based on the 2020 decennial census) will be considered one region type, and the legislative districts beginning in 2023 (the first year of districts based on the 2020 decennial census) will be considered another region type. Although the districts will have the same numbers for both region types, because the districts cover different geographic areas, they will not be comparable in the multiyear search feature. That is, you will not be able to compare the funded enrollment of Head Start in Senate District 52 in 2022 with the funded enrollment of Head Start in Senate District 52 in 2023. Because the geographic areas of the two examples of District 52 are not the same, such a comparison would be misleading.

Web resources