Illinois , April 2012 In Illinois, I-39 begins at
I-55 north of
Bloomington–Normal, Illinois, less than one mile east from the intersection of I-74 and I-55 that runs around the city of Normal. US 51 splits from I-55, joining I-39; exit 2 marks the northern terminus of the
US 51 business route. From Normal northward, I-39 runs northward largely through rural areas. At exit 8, the route forms the southern terminus of
Illinois Route 251 (IL 251), which was derived from the original routing of US 51. In
Oglesby in central
LaSalle County, I-39 passes next to
Starved Rock State Park, the busiest state park in Illinois. North of the park, it crosses the
Illinois River over the
Abraham Lincoln Memorial Bridge; at long, it is the longest bridge in the state. Just north of the river, I-39 passes between the cities of
LaSalle and
Peru; as it intersects
I-80 and
US 6, it makes its southernmost connections with the Chicago region. North of I-80, the wind turbines of the
Mendota Hills Wind Farm (the first commercial wind farm in Illinois) can be seen from milepost 72 at
Mendota north to near
Paw Paw. As I-39 continues northward, I-39 also intersects
US 52 and
US 30. In
Ogle County, I-39 intersects with
I-88 (
IL 110), connecting I-39 to both Chicago and the Quad Cities regions. As it intersects
IL 38,
IL 64, and
IL 72, I-39 connects with the DeKalb–Sycamore region and far west suburbs of the Chicago area. As I-39 crosses into Winnebago County, the Baxter Road exit (exit 115) is the final exit before I-39 joins the
US 20 freeway bypass in Rockford. Approximately a mile east of the Alpine Road/US 20 interchange, I-39 joins US 20, moving from nearly entirely farmland to medium-density populated areas. After heading northeast for approximately , US 20 splits from I-39/US 51; a mile northward, I-39/US 51 runs concurrently with I-90 (
Jane Addams Memorial Tollway). Though signed as I-39/I-90, the concurrency follows the mileposts of I-90. Though I-39 itself is not tolled, the
Illinois Tollway collects tolls on the I-90 portion, including two ramp interchanges and an open-road toll plaza between Rockton and South Beloit. At exit 1 (
IL 75) in
South Beloit, US 51 splits from I-39 to join IL 75; westward, it continues the route of IL 251 into Wisconsin. For all but one mile that I-39 is in Illinois, it runs concurrently with US 51.
Wisconsin I-39 enters Wisconsin in Rock County, concurrently with I-90. Bypassing Beloit to the east, it passes underneath the County Trunk Highway P bridge (CTH-P, Stateline Road). The tri-stack exit 185 provides access to Beloit through
WIS 81 and serves as the southern terminus of
I-43 (accessing Milwaukee and Green Bay). The northernmost interchange serving the Beloit region is CTH-S (Shopiere Road) at exit 183. About north of the I-43 interchange, I-39/I-90 is joined by
WIS 11 for as it bypasses
Janesville. In addition to the northern interchange that holds WIS 11, Janesville is also accessed by
US 14 and
WIS 26 (Milton Avenue). After crossing the
Rock River, I-39/I-90 has an interchange with
WIS 59, connecting it with
Edgerton (to the west) and
Milton (to the southeast). further north, the highway has an interchange with
US 151 (splitting Madison and
Sun Prairie); the northernmost Madison-area I-39 interchanges are US 51 (Madison and
DeForest) and WIS 19 (Sun Prairie and
Waunakee); CTH-V (West North Street) for DeForest serves as the last Dane County exit. I-39/I-90/I-94 enters
Columbia County north-northwest of CTH-V. From the county line northward, the highway returns to rural surroundings. after crossing the
Wisconsin River, exit 108 (
Wisconsin Dells) splits I-90/I-94 from I-39. For the first time since the US 20 Bypass in Rockford–Cherry Valley, I-39 is four lanes instead of six or eight. I-39 continues northward from
WIS 78 (which terminates at the interchange), routed towards Portage. I-39 connects with Portage through
WIS 33, crosses the Wisconsin River a second time, connects with
WIS 16; a third interchange rejoins I-39 with US 51. I-39 takes on the mileposts of the latter. After taking on US 51, I-39 continues northward, with few directional changes through
Marquette County and
Waushara County. In
Portage County, the highway continues its northward direction until it reaches the
Stevens Point region, where it bypasses the city to the east and north; four interchanges connect with the city (CTH-HH,
US 10/
WIS 66, Stanley Street, and Bus. US 51). From Stevens Point northward, I-39 largely parallels the path of the Wisconsin River and Lake DuBay. Following its entrance into
Marathon County,
WIS 153 connects to I-39 in
Mosinee, adjacent to the
Central Wisconsin Airport. The final north-south interchange of I-39 is exit 185 (
Bus. US 51) in
Rothschild, just before I-39 crosses the Wisconsin River. I-39 ends with exit 187, as
WIS 29 merges with US 51 (for approximately ); the latter highway continues north to its terminus at US 2 at the Wisconsin–Michigan border. == History ==