In Louisiana, Interstate 55 runs nearly 66 miles from south to north, from Interstate 10 near Laplace - roughly 20 miles west of New Orleans - to the Mississippi state line near Kentwood.
In Mississippi, I-55 runs 290.5 miles from the Louisiana border near Osyka to Southaven on the Tennessee border, just south of Memphis. The highway parallels U.S. 51 during its trek roughly through the center of Magnolia State.
The Mississippi section of Interstate 55 is defined in Mississippi Code ¡ì 65-3-3.
I-55 is often called the Mississippi Delta Highway because of its proximity to the Mississippi River.
I-55 lies entirely within the city of Memphis, passing through the southern and western parts of the city and providing a bypass of downtown for motorists who do not want to take Interstates I-240 and I-40 through downtown to cross the Mississippi River.
I-255 was the former numbering of I-240 between I-55 and I-40 through Midtown Memphis, Tennessee.
I-55 enters Arkansas from Tennessee as it crosses the Mississippi river. It overlaps I-40 for approximately 2.8 miles (4.5 km) in West Memphis. After separating from I-40, I-55 turns northward and runs to the Missouri border, via the intersection with the stretch of U.S. 63 that holds the future alignment of Interstate 555.
In Missouri, I-55 runs from the southeastern part of the state, at the Arkansas border, to St. Louis. Where Interstate 44 merges in and it joins Interstate 64 and Interstate 70 on the Poplar Street Bridge, which crosses the Mississippi River into Illinois.
A section of the I-55 in southern St. Louis County, Missouri has been named the "Rosa Parks Freeway" although the general public still refers to it as I-55.
On July 26th 2007 a small section of I-55 at the St. Louis city/county line was named "Thomas G. Smith Jr. Memorial Freeway".
Crossing over into Illinois, I-55, near the I-270/I-70 split, is referred to as the Paul Simon Freeway. This is in reference to the local politician Paul Martin Simon. Further north, between the St. Louis area and Springfield, IL, I-55 is named The Vince Demuzio Expressway in reference to Illinois state politician Vince Demuzio. I-55 parallels the historical Route 66 from East St. Louis to Chicago, passing near Springfield and Bloomington/Normal.
When the freeway was being planned during the 1960s, Illinois Governor Otto Kerner made an effort to have the road redirected near the larger city of Peoria instead of the more straightforward route through the Bloomington-Normal area. This ultimately failed plan was ridiculed in the press as the "Kerner Curve". The function of an Interstate highway connection between Springfield and Peoria was later filled by Interstate 155, which connects nearby Lincoln and Morton and forms a triangle between the three population centers in Central Illinois.
In the Chicago area, the expressway is referred to as the Adlai E. Stevenson Expressway in honor of one of Illinois' favorite sons. The general public typically refers to this freeway as either I-55 or "The Stevenson"; the terms are used interchangeably, but "The Stevenson" tends to be more popular in Chicago proper while I-55 is more commonly used in the suburbs.