Winnebago County I-90 enters Illinois concurrently with I-39 in
South Beloit as a six-lane expressway.
US Route 51 (US 51) joins Interstate at exit 1 (South Beloit); the between the exit and the state line is the only point where I-39 is not concurrent with US 51 in Illinois. The Jane Addams Memorial Tollway is immediately south of
Rockton and the South Beloit Toll Plaza (the northernmost toll plaza in Illinois). I-39/I-90 continues in nearly a north–south direction towards Rockford, and
IL 173 serves as its first exit; the Interstate pass through
Rock Cut State Park (among the largest in the state). The next exit (East Riverside Boulevard) forms the border between Rockford and Loves Park. US 20 makes its first two interchanges with I-90 in Winnebago County, both within of each other in the Rockford region. The first is with the State Street
US 20 business route connecting Rockford and Belvidere. The second is where I-90 splits with I-39/US 51, with the latter taking the path of the westbound US 20 bypass between Rockford and
Cherry Valley for approximately before it splits again to move southward. As the Jane Addams splits from I-39, I-90 takes a sharp change in direction from south to east; until it crosses through Jane Byrne Interchange in Chicago, it is signed only as I-90. The I-39/I-90 split between Rockford and Cherry Valley marks the point where I-90 and US 20 follow nearly parallel routing until their eastern terminus in Massachusetts (though sharing no concurrency). Eastward of the interchange, I-90 is fitted with center-mounted lighting. Shortly before entering Boone County, I-90 crosses the
Kishwaukee River.
Boone, McHenry, and Kane counties Shortly after entering Boone County, I-90 passes over US 20 and has two exits providing access to
Belvidere (accessing the eastern terminus of the US 20 business route). In addition to a westbound toll plaza, an
Illinois Tollway oasis is located here (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 exits the Rockford region and enters into more substantially rural surroundings, spacing exits much further apart. It changes to a southeast direction as it approaches
McHenry County, where the only exit is in unincorporated
Riley on
IL 23 ( south of
Marengo); to match the westbound Belvidere Toll Plaza, eastbound traffic passes through the Marengo Toll Plaza (approximately a mile eastward of IL 23). As I-90 enters
Kane County, the surroundings begin to transition from the farmland of Boone and McHenry counties towards various locations of the western Chicago suburbs (entering the
Golden Corridor of Illinois); within , the tollway has two exits. In
Hampshire, I-90 has its third interchange with US 20; an eastward exit is located with
IL 47 between
Pingree Grove and
Huntley. As I-90 approaches the
Fox Valley, it enters
Elgin, passing
Randall Road (the historic western terminus of the Chicago suburbs). After the interchange, I-90 expands from six to eight lanes in width and gradually turns east as it passes through the Elgin Toll Plaza (both directions) and
IL 31. After crossing the
Fox River, it passes
IL 25, its third interchange in the Elgin area.
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 (the first
SPUI exit on the tollway), 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 exit 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
I-355 (accessing the southern suburbs with access to I-55 and I-80). After passing the Eisenhower, I-90 expands from eight to ten lanes and turns gradually southeast towards Des Plaines (passing through
Rolling Meadows and
Arlington Heights). As it approaches Elmhurst Road (
IL 83 north of I-90), the tollway moves back to eight lanes as it passes directly north of
O'Hare International Airport; it widens back to ten lanes as it passes over US 45. The final exits for the I-90 tollway are in Rosemont, on Devon Avenue (westbound traffic) and River Road (eastbound).
Chicago Moving east of the
Tri-State Tollway (I-294) and crossing the
Des Plaines River, I-90 enters the Chicago city limits; no longer tolled, it becomes the
Kennedy Expressway with the
CTA Blue Line operating in the median. After crossing
IL 43, the Kennedy turns southeast, with I-94 joining it at
IL 50 in the
Mayfair neighborhood (marking the southern terminus of the
Edens Expressway). Eastward of IL 50 (Cicero Avenue), the highway operates 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). In the
Englewood neighborhood, I-90 splits from I-94, becoming the tolled Chicago Skyway. Following the southeast direction of the railroad tracks in the area, the six-lane 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==