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 | ||||||
| |||||||
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 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.