Redistricting authority:  
U.S. Congressional Districts – Legislative/Backup Commission. In the year following the census, the Illinois General Assembly is to draft legislation that would redistrict Illinois. The Governor has veto power.  However, if the Legislature hasn’t completed this task and the legislation hasn’t been signed into law by June 30, a Legislative Redistricting Commission shall be constituted by July 10.  The Commission will consist of 8 members, no more than 4 of whom may belong to the same political party. The majority and minority leaders in each House each get to appoint one representative and one person who is not a member of the General Assembly. The members of the Commission chose a chairman and vice chairman. They have until August 10 to file a redistricting plan with the Secretary of State approved by at least 5 of the members.  If they don’t come up with a plan by September 1, the Supreme Court submits the names of 2 people not of the same political party, and the SoS randomly draws the name of one of them by September 5 to serve as the 9th member of the Commission. The Commission then has until October 5th to file a redistricting plan with the Secretary of State approved by at least 5 members.  Once it’s filed with the Secretary of State, it has the force of law.

State Legislative Districts – Legislative. Same as above.