Where's the river, you might ask? At Kaskaskia Island, the Missouri-Illinois border is on the "wrong" (west) side of the Mississippi River. The river changed course on the Missisippi in the 19th Century.
The photo on Route U (above) was taken just a few hundred feet east of its intersection with US 61, indicating just how short Route U is. The white sign on the bridge says "Illinois State Line." (closeup, right) James Baughn reports that there is no Route U marker along the road itself in either direction.
Photos courtesy of James Baughn