U.S. Route 51

Southern terminus of US 51 at US 61, LaPlace

US 51 begins at the intersection with US 61 in Laplace and heads northeast. It intersects I-10 before running concurrently with I-55. Near the interchange with I-12, the route splits from I-55. It intersects US 190 in Hammond and remains running parallel with I-55 before entering Mississippi. In the 1930s, this highway was called Jefferson Davis Highway.[4]

US 51 enters Mississippi from Louisiana in Osyka and runs parallel with I-55. It intersects US 98 in McComb and US 84 south of Brookhaven. Northwest of Crystal Springs, it runs concurrently with I-55 and then splits at the interchange with I-20 in Jackson. The highway then runs through Jackson, intersecting US 80. Outside Ridgeland, it passes under I-55 as it continues northeast. It continues through Canton, Pickens, Goodman, and Durant. The highway continues to run along I-55, intersecting US 82 in Winona and US 278 in Batesville. The route passes under I-69 before entering Tennessee.

The Mississippi section of US 51 is defined at Mississippi Code Annotated § 65-3-3.

US 51 enters Tennessee from Mississippi and travels through Memphis. It intersects I-55 and then I-240 before intersecting US 78. It then runs concurrently with US 79 before intersecting I-69. As it exits Memphis, it intersects I-40 and heads northeasterly. In Dyersburg, it runs concurrently with US 412 for a half a mile before intersecting I-155's eastern terminus. US 51 then continues northeasterly before entering Kentucky. US 51 between Memphis and Kentucky is planned on running concurrently with I-69.

US 51 enters Kentucky at Fulton, running concurrently with I-69 and continues northward through the towns of Clinton, Bardwell and Wickliffe to the Ohio River. The route intersects and runs concurrently with US 62 before separating from it in Cairo. Along the way it also intersects US 60. The route then enters Illinois before running concurrently with I-57.

US 51 between Mounds and Cairo, during the Great Mississippi Flood of 1927

US 51 enters Illinois from Kentucky at the city of Cairo. The route heads northward to a village near Cairo called Mounds, and shares the pavement with I-57, following it for 24 miles (39 km) to Dongola, before splitting and heading north. The route remains two lanes from Dongola to just before Assumption with the exception of a 10-mile (16 km) section between Centralia and I-64.

North of Assumption, US 51 becomes an expressway to Decatur. In Decatur, US 51 follows I-72 to bypass town. US 51 leaves I-72 after eight miles (13 km), and heads north to Bloomington–Normal as an expressway. At Bloomington–Normal, US 51 follows I-74 for a mile, then I-55 for seven miles (11 km), before following I-39 for 140 miles (230 km).

US 51 follows I-39, intersecting I-80 and I-88 along the way. The highway also follows US 20 south of Rockford (while still following I-39). I-39/US 51 joins I-90, making US 51 one of the only toll roads in Illinois that is a U.S. Highway. US 51 exits I-39/I-90 just a mile south of the Wisconsin state line. US 51 follows Illinois Route 75 (IL 75) west to the intersection of IL 251, then turns north through South Beloit to enter Wisconsin.

Northern terminus of US 51 at US 2 in Hurley, WI

In the state of Wisconsin, US 51 enters from Illinois at Beloit. US 51 splits off from I-39/I-90 in South Beloit, Illinois and continues northward through Janesville and Edgerton. In Edgerton, US 51 rejoins I-39/I-90 for 3.5 miles (5.6 km) before splitting off towards Stoughton and McFarland. US 51 runs almost parallel to I-39/I-90 through the eastern portion of Madison, crosses the Interstate in DeForest, and finally rejoins I-39 again at Portage. US 51 runs concurrently with I-39 until I-39's terminus in Wausau and continues on as a mixture of freeway and expressway until just north of the interchange with US 8. From there through Hazelhurst, US 51 is a two-lane road with sporadic three-lane sections (which were constructed in 2008). US 51 expands to four lanes, with a central fifth turn lane from Hazelhurst to Arbor Vitae; north of Arbor Vitae it returns to two lanes and continues to its northern end in Hurley, where it terminates at US 2.