Illinois Route 21
Milwaukee Avenue Riverside Drive
IL 21 highlighted in red
Route information
Maintained by IDOT
Length	28.13 mi[1] (45.27 km)
Existed	November 5, 1918[2]–present
Major junctions
South end	IL 43 in Niles
Major intersections	US 14 in Niles US 45 in Prospect Heights US 45 in Lincolnshire I-94 Toll in Gurnee
North end	US 41 in Gurnee
Location
Country	United States
State	Illinois
Counties	Cook, Lake
Highway system
Illinois State Highway System Interstate US State Tollways Scenic
← US 20 → IL 22

Illinois Route 21 (IL 21) is an arterial north–south state highway in northeastern Illinois. It runs from Illinois Route 43 (Harlem Avenue) in Niles to U.S. Route 41 (Skokie Highway) north of Gurnee. Illinois 21 is 28.13 miles (45.27 km) long.^[1]

Along most of its length, Illinois 21 is called Milwaukee Avenue. North of Gurnee, it is called Riverside Drive.

Route description

Illinois 21 was the principal route to Milwaukee, Wisconsin before the construction of both the Skokie Highway and the Tri-State Tollway (Interstate 94 and Interstate 294). The towns of Glenview, Libertyville, and Gurnee are principally located along this road. It follows the Des Plaines River for its entire length, and overlaps U.S. Route 45 between Lincolnshire and Prospect Heights.

South of Illinois 43, Milwaukee Avenue remains a major arterial road until it reaches the downtown area of Chicago, where its historical terminus at Lake Street has been moved back to Grand Avenue. It is one of the few diagonal streets in the grid street layout of Chicago.

History

SBI Route 21 ran from Chicago to Antioch along Milwaukee Avenue and current Illinois Routes 43, 83 and 137. In Chicago, it also ran along Elston Avenue. In 1940, the route was moved to a new route to Grayslake, and then continued to Antioch. In 1963, Illinois 21 was dropped entirely from Grayslake to Antioch, and in 1972, it was shortened further to its current southern terminus at Illinois 43. The next year, Illinois 21 was rerouted to Gurnee. Illinois 83 and 137 replaced the old Route 21 to (and through) Grayslake.^[2]

Major intersections

County	Location	mi[3]	km	Destinations	Notes
Cook	Niles	0.0	0.0	IL 43 (Harlem Avenue)
		1.9	3.1	US 14 (Dempster Street)	Grade-separated interchange
		3.0	4.8	IL 58 (Golf Road)
	Prospect Heights	7.3	11.7	US 45 south (Des Plaines River Road)	South end of US 45 overlap
		7.6	12.2	Willow Road, Palatine Road to I-294 Toll	Grade-separated interchange
	Wheeling	10.0	16.1	IL 68 (Dundee Road)
Cook–Lake county line		11.0	17.7	Lake Cook Road	Grade-separated interchange
Lake	Lincolnshire	14.2	22.9	IL 22 (Half Day Road)
		14.5	23.3	US 45 north	North end of US 45 overlap
	Vernon Hills	17.2	27.7	IL 60 (Town Line Road)
	Libertyville	20.2	32.5	IL 176 (Park Avenue)
		21.8	35.1	IL 137 (Peterson Road, Buckley Road)
	Gurnee	24.7	39.8	IL 120 (Belvidere Road)	Grade-separated interchange
		25.8	41.5	I-94 Toll west (Tri-State Tollway) – Wisconsin	No access from or to I-94 east; I-94 exit 10
		27.0	43.5	IL 132 (Grand Avenue)
		28.13	45.27	US 41 (Skokie Highway)
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus       Incomplete access