The same calculus used to make that argument for Wisconsin suggests gerrymandering in Illinois is tepid by comparison. 

That conclusion flies in the face of the deeply held conviction among many Republicans that mapmaking foul play is the prime reason why powerful Illinois House Speaker Michael Madigan and fellow Democrats have for years remained firmly in control of both the Illinois House and Senate.

To be sure, the analysis of Illinois voting data in no way suggests that majority Democrats who drew the latest legislative maps here did so without putting a thumb on the scale. But the data points to the prime motivation being the protection of incumbents, be they Democrats or Republicans, and a variant of manipulation that the Supreme Court is not being asked to weigh in on. 

In recent election cycles, more than 90 percent of races for the Illinois House were either uncontested or involved only token challenges to an incumbent. That phenomenon benefits Democrats in the Chicago area, where the bulk of the state's population resides, and Republicans Downstate. 

"Illinois is really screwed up, but it's not as screwed up as Wisconsin," said Cynthia Canary, the former executive director of Change Illinois, which pushed to get a redistricting reform proposal on the November 2016 ballot, only to see it blocked by the Illinois Supreme Court. "There's a multitude of factors that come into play." 

One of those factors also lies at the heart of the Wisconsin case before the Supreme Court. It is a mathematical formula known as the "efficiency gap," a measurement of vote distribution developed by Nicholas Stephanopoulos, an assistant professor at the University of Chicago Law School, and Eric McGhee, a research fellow at the nonpartisan Public Policy Institute of California.

Designed to determine whether gerrymandering has enabled one political party to unduly extend its power, the formula compares the difference in so-called wasted votes—either those cast for a losing candidate or those cast for the victor in excess of what was needed to win. The election favors the party with fewer wasted votes, Stephanopoulos and McGhee wrote.

Read more at Crain's Chicago Business