Interstate 39

Interstate 39
I-39 highlighted in red
Route information
Maintained by IDOT, ISTHA and WisDOT
Length	306.14 mi[1] (492.68 km)
Existed	1986–present
NHS	Entire route
Major junctions
South end	I-55 / US 51 in Normal, IL
Major intersections	I-80 in LaSalle, IL I-88 Toll / IL 110 (CKC) in Rochelle, IL I-90 Toll in Cherry Valley, IL I-43 / WIS 81 in Beloit, WI I-94 / WIS 30 in Madison, WI I-90 / I-94 / WIS 78 in Portage, WI
North end	US 51 / WIS 29 near Rothschild, WI
Location
Country	United States
States	Illinois, Wisconsin
Counties	IL: McLean, Woodford, Marshall, LaSalle, Lee, Ogle, Winnebago WI: Rock, Dane, Columbia, Marquette, Waushara, Portage, Marathon
Highway system
Interstate Highway System Main Auxiliary Suffixed Business Future
Illinois State Highway System Interstate US State Tollways Scenic
Wisconsin State Trunk Highway System Interstate US State Scenic Rustic
← IL 38 IL → US 40 ← WIS 38 WI → WIS 39

Interstate 39 (I-39) is a north–south Interstate Highway in Illinois and Wisconsin that runs from an interchange at I-55 in Normal, Illinois, to State Trunk Highway 29 (WIS 29) approximately six miles (9.7 km) south of Wausau, Wisconsin.^[2][3] In total, Interstate 39 is 306.14 miles (492.68 km) long.^[1] In Illinois, the route has a total length of 140.82 miles (226.63 km)^[4]; in Wisconsin, I-39 has a distance of 182 miles (293 km).

Among the newest Interstate Highways in Illinois, I-39 was completed in 1992. Designed to replace U.S. Route 51 (US 51) with an Interstate-grade freeway, the highway runs concurrently with US 20 in Rockford before joining I-90. From Rockford to Portage, Wisconsin, I-39 and I-90 run concurrently. From Madison to Portage, I-94 joins the two; at 29 miles (47 km), the three-way concurrency is the longest in the country. From Portage northward, US 51 rejoins I-39, and the Interstate uses its mileposts northward.