Interstate 90 in Illinois

Interstate 90 (I-90) in the US state of Illinois runs roughly northwest-to-southeast through the northern part of the state. Entering Illinois at the Wisconsin state line in South Beloit, it passes through the Rock River Valley and the suburbs of Rockford, where it turns eastward, heading towards Chicago through farmland west of the Fox River Valley and through medium-density suburbs west of O'Hare International Airport. After entering through Downtown Chicago, I-90 passes through the heart of the industrial southeast side of Chicago before entering Indiana, crossing the Calumet River on the Chicago Skyway toll bridge.

In Illinois, I-90 consists of four major segments, including the Jane Addams Memorial Tollway (prior to 2007, the Northwest Tollway) from South Beloit to O'Hare Airport. Within Chicago, I-90 becomes the Kennedy Expressway from O'Hare to the Jane Byrne Interchange, where it becomes the Dan Ryan Expressway. In the Englewood neighborhood, I-90 splits from the Dan Ryan Expressway to become the Chicago Skyway toll bridge, remaining elevated until it crosses into Indiana. The Jane Addams and Chicago Skyway are toll roads maintained by the Illinois State Toll Highway Authority (ISTHA) and the Skyway Concession Company (SCC), respectively. The remainder of the highway is maintained by the Illinois Department of Transportation (IDOT). The current routing of I-90 in Illinois is 123.89 miles (199.38 km) long.

The Illinois routing of I-90 runs concurrently with two other Interstates, carrying I-39 (and US 51) from the Wisconsin border to an interchange between Rockford and Cherry Valley. In Chicago, I-90 carries I-94 for approximately 2⁄3 the length of the Kennedy Expressway and the entire length of the Dan Ryan Expressway. I-290 (Dwight D. Eisenhower Expressway) is an auxiliary Interstate Highway that has termini at two major points within I-90.