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Overview

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 a state as practicable.

The founders designed the U.S. House of Representatives to represent the people rather than the states. Article I, Section II of the Constitution provides each state at least one U.S. Representative, while the size of a state’s delegation to the House depends on its total population. With the aim of dividing representation among the states proportionately, Congress based apportionments on changes in state population as recorded in each decennial census since 1790. In order to keep the House at a manageable number, Congress set the size of the House at 435 voting Members.

Source of definition:

Date of definition: July 2012

Note: After each decennial census conducted by the U.S. Census Bureau, the U.S. congressional districts for each state are redrawn by the legislature of the state, the new districts are the basis for the next general election, and the new districts take effect in the U.S. Congress after that election. (For example, the decennial census was conducted in 2010; the new districts were redrawn in 2011; they were used as the basis for the general election in November 2012; and they took effect with the beginning of the subsequent U.S. Congress in January 2013.)

Note on number of legislative districts and yearly changes in legislative districts: Based on the reapportionment that was conducted after the 2000 decennial census, Illinois was apportioned 19 congressional districts. After the redrawing of the district boundaries by the Illinois legislature in 2001, the new districts took effect with the 108th Congress in January 2003. Neither the number nor the boundaries of congressional districts change within the period of a decennial census.

However, after the 2010 decennial census, both the number and boundaries of the congressional districts changed. Based on the reapportionment, Illinois was apportioned 18 congressional districts (a loss of one from the previous decennial census). The state legislature redrew the congressional district boundaries in 2011, the new districts served as the basis of the 2012 general election, and the new districts took effect with the 113th Congress session 1 of 2013. The new districts will continue in effect through the 117th Congress session two of 2022.

Although congressional district boundaries do not change between decennial censuses, representatives themselves do, as they lose elections, retire, resign, or die in office. Thus some congressional districts may have two representatives in a single session; for example, a representative who resigned and the representative who was appointed in the resignee’s place. In its list of congressional districts with representatives’ names and in the U.S. Federal Congressional District options on the search pages, IECAM tries to keep as up-to-date as possible with these changes. IECAM retains an archive of lists of representatives from previous congresses. In these archived lists, for those districts that had two representatives in a single session, IECAM will retain the name of one representative only, usually the latest-serving representative.

Note on data availability by U.S. Federal Congressional Districts: Almost all site-based data (e.g., child care) and almost all demographic data (e.g., population) are presented by U.S. federal congressional district in IECAM. Non-site-based data (e.g., early intervention) are not presented by U.S. federal congressional district.

Note on comparing congressional districts across decennial censuses. In IECAM’s online database and multi-year search feature, the congressional districts up through 2012 (the last year of districts based on the 2000 decennial census) will be considered one region type, and the congressional districts beginning in 2013 (the first year of districts based on the 2010 decennial census) will be considered another region type.

Because these region types have different numbers of district areas (19 for the post-2000 census; 18 for the post-2010 census), and because the districts cover different geographic areas, it is not possible to compare data for post-2000 census districts and post-2010 census districts. For example, you cannot compare data on PFA capacity or population of children for Congressional District 15 in 2010 with the data on PFA capacity or population of children for Congressional District 15 in 2014. Such a comparison would be misleading.

However, you are able to compare data for different years that apply to the post-2000 census districts and for different years that apply to the post-2010 census districts. For example, you can compare data on PFA capacity or population of children for Congressional District 15 in 2010 and in 2011; and you can compare the same data for Congressional District 15 in 2013 and in 2014.

Note: View a list of U.S. Federal Congressional districts in Illinois, with names of legislators, for the current congress and previous congresses.

Census 2010

See the “Overview” section for general information about congressional districts.

Source of definition: U.S. Census Bureau, Geography Division. Geographic Terms and Concepts – Congressional District

Date of definition: July 2012

Note on Census 2010 districts: After each decennial census conducted by the U.S. Census Bureau, the U.S. congressional districts for each state are redrawn by the legislature of the state, the new districts are the basis for the next general election, and the new districts take effect in the U.S. Congress after that election.

Thus, after the 2010 Census, the Illinois congressional 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 U.S. Congress in January 2013.

The Census 2010 districts are in effect from:
113th Congress, Session One, 2013
through
117th Congress, Session Two, 2022

Note on number of congressional districts and yearly changes in congressional districts: See the note in the “Overview” section for information on this topic.

Note on data availability by U.S. Federal Congressional Districts: Almost all site-based data (e.g., child care) and almost all demographic data (e.g., population) are presented by U.S. federal congressional district in IECAM. Non-site-based data (e.g., early intervention) are not presented by U.S. federal congressional district.

Note on comparing congressional districts across decennial censuses: See the note in the “Overview” section for information on this topic.

Note: View a list of U.S. Federal Congressional districts in Illinois, with names of legislators, for the current congress and previous congresses.

Census 2000

See the “Overview” section for general information about congressional districts.

Source of definition:

Date of definition: July 2012

Note on Census 2000 districts: After each decennial census conducted by the U.S. Census Bureau, the U.S. congressional districts for each state are redrawn by the legislature of the state, the new districts are the basis for the next general election, and the new districts take effect in the U.S. Congress after that election.

Thus, after the 2000 Census, the Illinois congressional 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 U.S. Congress in January 2003.

The Census 2000 districts were in effect from:
108th Congress, Session One, 2003
through
112th Congress, Session Two, 2012

Note on number of congressional districts and yearly changes in congressional districts: See the note in the “Overview” section for information on this topic.

Note on data availability by U.S. Federal Congressional Districts: Almost all site-based data (e.g., child care) and almost all demographic data (e.g., population) are presented by U.S. federal congressional district in IECAM. Non-site-based data (e.g., early intervention) are not presented by U.S. federal congressional district.

Note on comparing congressional districts across decennial censuses. See the note in the “Overview” section for information on this topic.

Note: View a list of U.S. Federal Congressional districts in Illinois, with names of legislators, for the current congress and previous congresses.

Web Resources: Geographic Regions