How Redistricting Works


The Illinois Constitution of 1970 mandates that legislative maps are changed every 10 years. Additionally, the Federal government also requires that a U.S. census be commissioned ever 10 years as well to record data on demographic and socio-economic changes in the country. The census data is used as a mechanism so that the newly designed maps are legal and abide by the Voting Rights Act of 1965. This piece articulates how new legislative districts maps, or redistricting, is validated by Illinois state government.


The year after the U.S. Census is taken and adopted is when map making first begins. Once the state has the data from the year prior, the House and the Senate each work to design their own legislative maps; a map for House districts and a map for Senate districts.

Essentially, the maps need to be passed by both chambers before July 1 and then signed by the Governor to be validated. If this does not happen, the process is referred to a Redistricting Commission consisting of four Democrats and four Republicans. The Commission further deliberates and must meet an agreement before August 10. If there is a stalemate (which is normally what happens) the process is referred to the Illinois Supreme Court.

The Illinois Supreme court provides the names of one Democrat and one Republican to the Illinois Secretary of State to be randomly drawn in an attempt to split the partisan gridlock. Either the Democrats or Republicans will then hold a one person majority on the Redistricting Commission based on whosever name is drawn. In effect, the partisan gridlock will be broken and the Commission will be able to come to a consensus on redistricting. The new maps must be validated by the now nine member Redistricting Commission by October 5th. Figure 1 below illustrates this entire process.

Figure 1: Process map created by Prairie State Policy

Previous Years

The map drawing process normally is not passed by a wide consensus and is usually referred to the Redistricting Commission to be completed. This is because party rule in both legislation chambers and the executive branch has historically been split and no party has had majority in the House, Senate and control of the Governorship all at once. However, whoever has control of the legislative chambers and the governorship at the beginning of the decade usually become the beneficiaries of legislative districts for the next 10 years. Figure 2 below illustrates what party eventually won control of the process the last 40 years.

Figure 2: Illustration created by Prairie State Policy

The key takeaway from redistricting process is that one party would have to control both legislative chambers and the governorship in order for a stalemate to be avoided. If this does not happen, which is the norm, then who controls the re-mapping process is left entirely to chance based on the random draw of a single name.


The making of new legislative district maps every 10 years is a complex process that requires a meticulous approach from lawmakers and policy wonks. As previously noted, redistricting must meet certain federal guidelines to avoid excessive gerrymandering, which is manipulating the re-drawing of districts to completely favor one party over the other. So while validation of the new maps can be achieved through multiple routes, the actual drawing of the maps itself is part of the “sausage making” in state government.

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