The northern terminus is at US 52 in rural Clayton County near the towns of Monona and Farmersburg near the intersection of US 52 and US 18.

It continues north from Marion to Central City, where the divided highway ends.

It continues north through Manchester and intersects Iowa 3 at the southern border of Clayton County west of Edgewood.

It overlaps Iowa 3 and goes northwest into Strawberry Point, where they separate.

Its original extent was statewide, starting at the Missouri state line south of Bloomfield and ending at the Minnesota state line north of Waukon.