Iowa Highway 128 is a highway entirely within Clayton County, in northeastern Iowa. Its western terminus is at Iowa Highway 13 northeast of Elkader. Its eastern terminus is at U.S. Route 52 north of Garnavillo. Iowa 128's route remains the same as when it was first designated.

Iowa Highway 128 begins a T-intersection with Iowa Highway 13 2 miles (3.2 km) north of Elkader. It passes through rolling farmland on the western edge of the Driftless Area, a geologically distinct area of northeastern Iowa characterized by undulating terrain, high bluffs, and low river valleys. It travels 7 miles (11 km) to the east until it ends at an intersection with U.S. Route 52 1 mile (1.6 km) north of Garnavillo.

By 1926, Primary Road No. 128 existed in its current location; however, the eastern end of the route was along Primary Road No. 20, which became U.S. Route 52 in the coming decade.

The entire route is in Clayton County.