Iowa 51 begins at the intersection of Tilden and Lawler Streets in Postville.

US 18 and US 52 form the southern and western forks of the intersection, Tilden Street continues east, and Iowa 51 begins heading north along Lawler Street through Postville's downtown area.

The highway crosses a line of the Dakota, Minnesota and Eastern Railroad and leaves Postville heading in an almost directly northward alignment.

The only curves along the route come as the highway descends into and then ascends out of the Yellow River valley.

The route was fully paved by 1935, with the segment from the Yellow River south to Postville being repaved in 1969.