Louisiana 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.
Mississippi 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.
Tennessee 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.
Kentucky 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.
Illinois 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 to
Dongola, before splitting and heading north. The route remains two lanes from Dongola to just before
Assumption with the exception of a 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 , and heads north to
Bloomington–
Normal as an expressway. At Bloomington–Normal, US 51 follows
I-74 for a mile, then
I-55 for , before following
I-39 for . 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.
Wisconsin 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 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. ==Major intersections==