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Overview
State Legislative Districts (SLDs) are the areas from which members are elected to state legislatures. The U.S. Census Bureau first reported data for 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 state legislature.

The legislative power of the State of Illinois 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.

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

Source of definition:

Date of definition: July 2012

Note: 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. (For example, the decennial census was conducted in 2010. The new districts were redrawn in 2011, used as the basis for the general election in November 2012, and took effect with the beginning of the subsequent general assembly in January 2013.)

Note: For additional information, visit the Illinois General Assembly Web site.

Note on  number of legislative districts and yearly changes in legislative districts: As noted above, there are 59 Senate districts and 118 House districts in Illinois. The number of districts does not change. Nor do the boundaries of districts change within the period of a decennial census. However, legislators themselves change from year to year, as senators and representatives lose elections, retire, resign, or die in office. Thus some legislative districts may have different legislators from year to year; or they may have two legislators in a single session, as for example, a legislator who resigned and the legislator who was appointed in the resignee’s place.

IECAM maintains a Legislative District Information page that provides lists of legislative districts with legislators’ names for each session of the General Assembly. IECAM tries to keep these lists as up-to-date as possible. In these lists, for those districts that had two legislators in a single session, IECAM will retain the name of one legislator only, usually the latest-serving legislator.

Note on  data availability by State House Districts and Senate Districts: Almost all site-based data (e.g., child care) and almost all demographic data (e.g., population) are presented by state house district and senate district in IECAM. Non-site-based data (e.g., early intervention) are not presented by state house district and senate district.

Note on  comparing legislative districts across decennial censuses. In IECAM’s online database and in the multi-year search feature, the legislative districts up through 2012 (the last year of districts based on the 2000 decennial census) will be considered one region type, and the legislative districts beginning in 2013 (the first year of districts based on the 2010 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 multi-year search feature. That is, you will not be able to compare, for example, the funded enrollment of Head Start in Senate District 52 in 2012 with the funded enrollment of Head Start in Senate District 52 in 2013. Because the geographic areas of the two examples of District 52 are not the same, such a comparison would be misleading.

Note: View a list of Senate and House districts with names of legislators, for the current general assembly and previous general assemblies.

Post-Census 2010 legislative districts
State Legislative Districts (SLDs) are the areas from which members are elected to state legislatures. The U.S. Census Bureau first reported data for 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 state legislature.

Source of definition:

Date of definition: July 2012 Note: For additional information, visit the Illinois General Assembly Web site.

Note on Census 2010 districts: 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 IL state house and senate districts were redrawn in 2011. These districts were 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.

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

Note on  Census 2010 districts reported in IECAM: 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) in order to provide a baseline comparison for later data.

Note on  number of legislative districts and yearly changes in legislative districts: There are 59 Senate districts and 118 House districts in Illinois. See the “Overview” notes for additional information on legislative districts and changes in legislative districts place.

Note on  data availability by State House Districts and Senate Districts: Almost all site-based data (e.g., child care) and almost all demographic data (e.g., population) are presented by state house district and senate district in IECAM. Non-site-based data (e.g., early intervention) are not presented by state house district and senate district.

Note on  Census 2000 districts: See the “Post-Census 2000 legislative districts” notes for information about those districts.

Note on comparing legislative districts across decennial censuses: In IECAM’s online database and in the multi-year search feature, the legislative districts up through 2012 (the last year of districts based on the 2000 decennial census) will be considered one region type, and the legislative districts beginning in 2013 (the first year of districts based on the 2010 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 multi-year search feature. That is, you will not be able to compare, for example, the funded enrollment of Head Start in Senate District 52 in 2012 with the funded enrollment of Head Start in Senate District 52 in 2013. Because the geographic areas of the two examples of District 52 are not the same, such a comparison would be misleading.

Note: View a list of Senate and House districts with names of legislators, for the current general assembly and previous general assemblies.

Post-Census 2000 legislative districts
State Legislative Districts (SLDs) are the areas from which members are elected to state legislatures. The U.S. Census Bureau first reported data for 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 state legislature.

Source of definition:

Date of definition: July 2012

Note: For additional information, visit the Illinois General Assembly Web site.

Note on  Census 2000 districts: 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 2000 Census, the IL state house and senate districts were redrawn in 2001. These districts were used as the basis for the general election held in November 2002. They took effect with the beginning of the subsequent general assembly in January 2003.

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).

Note on  number of legislative districts and yearly changes in legislative districts: There are 59 Senate districts and 118 House districts in Illinois. See the “Overview” notes for additional information on legislative districts and changes in legislative districts place.

Note on data availability by State House Districts and Senate Districts: Almost all site-based data (e.g., child care) and almost all demographic data (e.g., population) are presented by state house district and senate district in IECAM. Non-site-based data (e.g., early intervention) are not presented by state house district and senate district.

Note on Census 2010 districts: See the “Post-Census 2010 legislative districts” notes for information about those districts.

Note on comparing legislative districts across decennial censuses: In IECAM’s online database and in the multi-year search feature, the legislative districts up through 2012 (the last year of districts based on the 2000 decennial census) will be considered one region type, and the legislative districts beginning in 2013 (the first year of districts based on the 2010 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 multi-year search feature. That is, you will not be able to compare, for example, the funded enrollment of Head Start in Senate District 52 in 2012 with the funded enrollment of Head Start in Senate District 52 in 2013. Because the geographic areas of the two examples of District 52 are not the same, such a comparison would be misleading.

Note: View a list of Senate and House districts with names of legislators, for the current general assembly and previous general assemblies.

Web Resources: Geographic Regions