The route heads north along Hickory Street and out of town parallel to the western bank of the Little Sioux River.

[2] It heads to the north-northeast for 20 miles (32 km) through the Woodbury County communities of Oto and Anthon, and crosses the Little Sioux southwest of Correctionville.

[1] At Correctionville, Iowa 31 intersects U.S. Highway 20 and then curves around following the eastern bank of the Little Sioux.

At Quimby, the route turns east and travels 4 miles (6.4 km) to its northern end at U.S. Highway 59.

[4] By 1952, Iowa 31 had moved onto its current alignment, where it remains to this day.