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 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 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.

Route description

Winnebago County

I-90 enters Illinois concurrently with I-39 in South Beloit (the northernmost city in Illinois) as a six-lane expressway. At south of the state line (marked as exit 1, South Beloit), I-39/I-90 has an interchange with Illinois Route 75 (IL 75); the interchange marks the point where US Route 51 (US 51) runs concurrently with I-39 until its southern terminus.

After an interchange northeast of the Rockford suburbs of Rockton and Roscoe, the Jane Addams Memorial Tollway starts with the South Beloit Toll Plaza (the northernmost toll plaza in Illinois). Through eastern Winnebago County, I-39/I-90 continues in nearly a north–south direction towards the eastern edge of Rockford. Before passing through Rock Cut State Park (among the largest in the state), the Interstate has an interchange with IL 173, accessing Machesney Park from the north; built in 2007, the interchange design was influenced by the location of the state park.

I-39/I-90 enters the city of Rockford with an interchange at exit 12 (East Riverside Boulevard), crossing the border between Rockford and Loves Park. Before exiting the county, the highway forms its two largest intersections west of I-290, with exit 15 (State Street), accessing the US 20 business route connecting Rockford and Belvidere. Exit 17, located between Rockford and Cherry Valley, is the point where I-90 splits from I-39 (taking US 51 with it) and forms the approach to the diverging-diamond interchange that starts the US 20 bypass around Rockford (U.S. Grant Highway); approximately southeast, I-39/US 51 splits again to move towards central Illinois. As the Jane Addams splits from I-39, I-90 takes a sharp change in direction from south to east; this also marks the point where I-90 and US 20 follow nearly parallel routing until their eastern terminus in Massachusetts (though sharing no concurrency).

From exit 17 to its intersection with the Edens Expressway (I-94), the highway is only signed as I-90. Eastward of the interchange, I-90 is fitted with center-mounted lighting. Shortly before entering Boone County, I-90 crosses the Kishwaukee River north of the village of Cherry Valley.

Boone, McHenry, and Kane counties

Shortly after entering Boone County, I-90 passes under US 20 and forms the southern border of Belvidere. Along with sharing one tolled exit with Cherry Valley (Irene Road), Belvidere has a second tolled exit (Genoa Road) which accesses the eastern terminus of the US 20 business route. In addition to a westbound toll plaza, an Illinois Tollway oasis is located westward of the latter exit (the sole example on I-90). The over-highway design of the oasis houses multiple vendors, allowing tollway travelers the options of resting, eating, and refueling from one location on the highway.

East of Belvidere, I-90 changes its direction from east to southeast. After exiting the Rockford region entirely, its surroundings become substantially rural, with exits spaced farther apart. Entering McHenry County, I-90 has only one exit: a tolled interchange with IL 23 (exit 36) in unincorporated Riley (accessing Marengo and Genoa). To match the westbound Belvidere Toll Plaza, eastbound traffic passes through the Marengo Toll Plaza (approximately a mile eastward of IL 23).

I-90 enters Kane County in Hampshire, forming its third intersection with US 20 (exit 42). Eastward, it crosses IL 47 (exit 47) between Pingree Grove and Huntley. As I-90 passes under IL 72 in Gilberts, the rural surroundings disappear as the highway becomes surrounded by a mix of residential, commercial, and industrial developments (along with large nature preserves). As I-90 approaches the Fox Valley, it enters Elgin (the third-largest city in Illinois to border I-90) with three exits accessing the city. After passing exit 52 (Randall Road), marking the historic western terminus of the Chicago suburbs, I-90 expands from six to eight lanes and gradually turns east as it passes through the Elgin Toll Plaza (both directions) and exit 54 (IL 31). After crossing the Fox River, I-90 passes through exit 56 (IL 25) at the Cook County border.

Suburban Cook county

After exiting Kane County, I-90 moves uphill as it enters Cook County, heading eastward towards I-290 (Eisenhower Expressway). Prior to its intersection with the Eisenhower, the highway passes through Hoffman Estates (including IL 59) and Schaumburg (each also have a westbound-only interchange). Eastward of the Barrington Road exit, I-90 is fitted with active traffic management gantries. I-290 has its northern terminus with I-90, as it becomes IL 53 north of the tollway.

To the north, the I-290 interchange (exit 68) provides access to many suburbs accessed by both US 12 and US 14. To the south, the Eisenhower provides expressway access to the city of Chicago, along with access to the southern suburbs through (I-355, I-294, and I-88). After exit 68, I-90 expands from eight to ten lanes and turns gradually southeast towards Des Plaines (passing through Rolling Meadows and Arlington Heights). Exit 73 (IL 83) is a diverging-diamond interchange; as it approaches the exit, I-90 moves to eight lanes as it passes directly north of O'Hare International Airport (crossing past the future I-490), widening back to ten lanes after crossing over US 12/US 45 (Mannheim Road). In Rosemont, the final exits for the Jane Addams Tollway are on Devon Avenue (westbound traffic) and River Road (eastbound); the final exit for both directions is exit 77 (Tri-State Tollway), which accesses I-294 and I-190 (an auxiliary leg of the Kennedy Expressway, connecting it to O'Hare Airport).

Chicago

After crossing the Tri-State Tollway (I-294) and crossing the Des Plaines River, I-90 enters the Chicago city limits and becomes the toll-free Kennedy Expressway. As the CTA Blue Line operates in the median, the Kennedy uses side-mounted lighting. Following exit 81A crossing Harlem Avenue (IL 43), the highway turns southeast in direction. In the Mayfair neighborhood, I-94 joins the Kennedy as it crosses under IL 50 (Cicero Avenue). Along with marking the southern terminus of the Edens Expressway, the combined I-90/I-94 takes on the mile markers of the latter highway. The Blue Line returns underground, with the center of the I-90/I-94 Kennedy operating with reversible express lanes, directing express traffic (in addition to the eight lanes of local traffic). Following the direction of the Chicago River, the Kennedy Expressway has its eastern terminus in the West Loop at the Jane Byrne Interchange (passing the Eisenhower Expressway).

After passing through the Jane Byrne Interchange, I-90/I-94 becomes the Dan Ryan Expressway. In contrast to the electronically controlled gates used by the Kennedy, the Dan Ryan is up to 14 lanes wide (with a center express section and outer lanes for local traffic). Moving nearly entirely in a north-south direction, the highway travels to the Englewood neighborhood, where I-90 splits from I-94 (returning to its own mile markers). In becoming the tolled Chicago Skyway, I-90 becomes six lanes for the first time since entering the Chicago suburbs as the highway follows the southeast direction of the railroad tracks in the area. The skyway is an elevated road linked to a bridge crossing the Calumet River.

As it exits Illinois, I-90 continues into Hammond, Indiana, (directly over US 20 and US 41) before moving back onto ground level as the Indiana Toll Road.

History

Jane Addams Memorial Tollway The Northwest Tollway portion of I-90 opened on August 20, 1958. Prior to the opening, the first vehicle to officially travel the new roadway was a covered wagon navigated by local resident John Madsen who took five days to make the journey.

On September 7, 2007, highway officials responding to an effort by state lawmakers renamed the Northwest Tollway to Jane Addams Memorial Tollway, after Jane Addams, the Nobel Peace Prize winner and founder of the Settlement House movement in the US.

The Illinois Tollway's 2005–2012 Congestion-Relief Program provided $644.1 million (equivalent to $ in ) in projects along the I-90 corridor. Projects included rebuilding and widening of the tollway between I-39 and Rockton Road, including a reconfiguration of the I-90/I-39 interchange. This construction started in 2008 and was completed by the end of 2009.

From 2013 to 2016, over $2 billion (equivalent to $ in ) was spent on rebuilding and widening the Jane Addams Memorial Tollway from I-39 to the Kennedy Expressway. The inside shoulders were widened for future transit opportunities, and active traffic management was incorporated into the corridor from IL 59 to the eastern end. In addition, almost all of the crossroad bridges were rebuilt and several interchanges were reconfigured/expanded. In 2019, a $33.4-million (equivalent to $ in ) interchange with IL 23 was added near Marengo to provide the first I-90 interchange in McHenry County.

Until 1978, I-90 was routed on the Congress Street Expressway (later named the Eisenhower Expressway) which was extended from the Loop to the interchange of the Northwest Tollway and IL 53. The Kennedy Expressway was signed only as I-94, and the portion of present-day I-90 between the Edens Expressway and IL 53 was not signed as an Interstate Highway. This provided a non-toll section of I-90 between Downtown Chicago and IL 53. The route designations were changed to their present form when I-90 was moved to follow the entire length of the Kennedy Expressway and the Jane Addams Tollway, and the original route was designated I-290.

In 2018, ISTHA raised the speed limit on I-90 from from the I-39 split to Randall Road. They also raised it from from Randall Road to Mount Prospect Road and raised it from from Mount Prospect Road to the Kennedy. The speed limit for buses is , and the speed limit for trucks is .

Chicago Skyway