States traversed: Wisconsin, Illinois, Kentucky, Tennessee, Mississippi, and Louisiana
US Route 51 forms the backbones of Wisconsin and Illinois, before cutting south through westernmost Kentucky, westernmost Tennessee, and central Mississippi, to end at US Route 61 just west of New Orleans, Louisiana. US Route 51 gave birth to the Interstate 39 corridor in central Wisconsin, southern Wisconsin, and northern Illinois, as well as the Interstate 55 corridor in Mississippi and Louisiana. Numbered mathematically halfway between US Route 1 and US Route 101, US Route 51 forms the halfway point for north-south highways in the contiguous United States. The northern end of US Route 51 sits at a trumpet interchange with US Route 2 in Hurley, Wisconsin, a town on the border with the Upper Peninsula of Michigan, not far from Lake Superior. US Route 51 heads south, doing its own thing in northern Wisconsin, but at Wausau, US Route 51 becomes the northern start of Interstate 39. US Route 51 follows the Interstate 39 corridor past Madison, Wisconsin, and Rockford, Illinois, until Interstate 39's southern end in Normal, Illinois. US Route 51 continues south on its own to pass through Decatur, Illinois, and Carbondale, Illinois, before crossing the Ohio River into westernmost Kentucky, at the river's westernmost extent. US Route 51 continues south into westernmost Tennessee and the Memphis area. US Route 51's time in Mississippi and Louisiana is spent hugging alongside Interstate 55. When Interstate 55 ends at Interstate 10 west of New Orleans, Louisiana, US Route 51 escapes onto a short surface road until US Route 61 soon cuts it off in LaPlace, Louisiana.
My photo for US Route 51 shows a northbound trailblazer in Anna, Illinois, at the junction with Illinois Route 146. This is in the southernmost portion of Illinois, one county north of the county home to Cairo in Illinois's southern tip. A long weekend in southern Illinois in November 2018, led me to stay at the Super 8 visible in the background of this photo. Clean signage and favorable lighting led to the serendipitous choice to photograph this sign assembly for my national collection.
Bonus photo: Here's a shot of the southern end of US Route 51 in La Place, Louisiana, looking north at the first trailblazer. US Route 61 heads from east to west past this southern terminus of US Route 51 here: