^Looking south at the Illinois River bridge just south of US Route 6 in Peru, November 2019.
Illinois Route 251 follows a long former alignment of US Route 51, from a point within a mile of the Wisconsin border, south to a point just north of Bloomington-Normal. It parallels Interstate 39, which carries the current alignment of US Route 51, for its entire length.
The northern end of Illinois 251 comes as US Route 51 diverts east along Illinois 75 to join Interstate 39. At this 4-way intersection, US Route 51 turns easterly along Illinois 75 right after crossing into Illinois from Wisconsin, while continuing south gives you the inception of Illinois Route 251...
Illinois 251 crosses Illinois 173 in Rockford's northern suburbs, where that route meets its western end...
Illinois 251 passes by Business US 20 in downtown Rockford...
Illinois 251 then meets the freewayUS Route 20 on the south side of Rockford...
Illinois 251 crosses Illinois 72 at Davis Junction...
Illinois 251 crosses Illinois 64 north of Rochelle...
Then, Illinois 38 comes from the east and joins Illinois 251 south into Rochelle...
At a makeshift folded diamondinterchange made out of two city blocks, Illinois 38 is transferred onto a road it uses to exit town to the west, which Illinois 251 crosses via an overpass: