^Looking north from Makanda, May 2025.
US Route 51 runs north-south down the central axis of Illinois, from Wisconsin to Kentucky. It runs from Beloit, Wisconsin, south through Rockford, LaSalle, Bloomington-Normal, Clinton, Decatur, Vandalia, and Cairo, among other locales.
US Route 51 enters Illinois from Beloit, Wisconsin (photo looks north):
US Route 51 enters Illinois from Beloit, Wisconsin (photo looks north):
Less than a quarter mile south of the state border, US Route 51 joins Illinois 75 east and creates Illinois 251, which operates as a surface road in its stead (photo looks north):
After just over a mile in South Beloit along Illinois 75, US Route 51 joins Interstates 39 and 90 south. For the section of US Route 51 concurrent with Interstate 39 between South Beloit and Bloomington-Normal, see the Interstate 39 page.
Interstate 39 ends on the north side of Bloomington-Normal, at Interstate 55. From there, US Route 51 joins Interstate 55 south...
US Route 51 and Interstate 55 are both joined by Interstate 74, and all three highways run southward concurrently along the west side of Bloomington-Normal:
Interstate 74 and US Route 51 split from Interstate 55 to head east around the south side of Bloomington:
Shortly after that, US Route 51 splits from Interstate 74 at an interchange where US Route 51 continues to the south, but the southern end of US Route 51's business alignment heads north:
US Route 51 continues from here as a rural expressway with grade crossings, but with exits to other major highways, like the exit to US Route 136 at Heyworth:
US Route 51 then bypasses Clinton to the west, but it creates a Business US Route 51 alignment that heads south into town:
US Route 51 crosses Illinois 10 on the west side of Clinton:
Then, US Route 51 crosses another route, Illinois 54, on the west side of Clinton:
US Route 51's business alignment comes back to US Route 51 on the south side of Clinton:
At a cloverleaf interchange on the north side of Decatur, US Route 51 joins Interstate 72 west:
Along the concurrency of Interstate 72 and US Route 51 is an interchange with Illinois 121:
At an interchange on the west side of Decatur, US Route 51 splits from Interstate 72 and crosses US Route 36 (which joins Interstate 72 west):
US Route 51, still a freeway, makes an interchange with Illinois 48, on the southwest side of Decatur:
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US Route 51 stops being a freeway south of Decatur, and it becomes a 4-way surface highway until three miles north of Pana. When US Route 51 does reach the vicinity of Pana, it joins Illinois 16 westward into town:
In Pana, US Route 51 and Illinois 16 together reach the southern end of Illinois 29:
On the south side of Pana, US Route 51 and Illinois 16 part ways, and US Route 51 heads south once again:
As US Route 51 enters Vandalia, it meets an interchange with Interstate 70:
After traveling just one more block to the south, US Route 40 and Illinois 185 join US Route 51 from the west:
US Route 51 splits from US Route 40 and Illinois 185, just after crossing the Kaskaskia River out of Vandalia:
In the small town of Sandoval, US Route 50 joins US Route 51 from the east:
After several blocks concurrent with US Route 51, US Route 50 splits away to continue westerly:
US Route 51 splits into a pair of one-way streets in Centralia, where it meets another pair of one-way streets carrying Illinois 161:
At Irvington, US Route 51 has a very short segment as an expressway, with a diamond interchange to Illinois 177:
US Route 51 meets Interstate 64 at a normal diamond interchange, with US Route 51 taking the form of the surface road, as it approaches the town of Ashley:
At Ashley, US Route 51 joins Illinois 15 west for a few miles:
Then, west of Ashley, US Route 51 splits from Illinois 15 to resume its southerly journey:
Near Tamaroa, US Route 51 crosses Illinois 154:
In DuQuoin, US Route 51 meets the eastern end of Illinois 152:
On the south side of DuQuoin, US Route 51 meets the western end of Illinois 14:
At DeSoto, US Route 51 crosses Illinois 149:
In downtown Carbondale, US Route 51 is a pair of one-way streets again, intersecting the pair of one-way streets carrying Illinois 13:
At Anna, US Route 51 crosses Illinois 146:
Near Dongola, US Route 51 joins Interstate 57 south:
Near Urbandale, US Route 51 splits from Interstate 57 by exiting onto Illinois 3 eastbound:
After less than a mile, US Route 51 reaches a T-intersection and turns right, where Illinois 37 to the left comes to an end, and the concurrent Illinois 3 also comes to an end:
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US Route 51, having turned southerly through Cairo, meets a junction with US Routes 60 and 62, which cross the Mississippi River and immediately turn to exit Illinois via a bridge over the Ohio River. This is at the southernmost junction in Illinois, right next to where the Ohio River empties into the Mississippi...
US Route 51 elects to turn left over the Ohio River, into Kentucky, sharing the bridge with US Routes 60 and 62...
