It begins at the Mississippi River in Clinton on the Mark Morris Memorial Bridge, where it continues as Illinois Route 136.

During the 1950s-1960s, the northern and southern ends of the route shifted slightly because nearby United States highways changed their alignments.

Iowa Highway 136 begins on the Mark Morris Memorial Bridge over the Mississippi River at Clinton.

North of Onslow, it passes through rural Jones County for 15 miles (24 km), crossing the Maquoketa River, before reaching Cascade and U.S. Route 151.

[1] Now in Dubuque County, Iowa 136 crosses the North Fork Maquoketa River and heads northwest towards Worthington.

[6] A year later, an Alternate U.S. Route 30 was designated over the old alignment of US 30 through Clinton, and Iowa 136 was pulled back to its old end.

[9][10] Shortly after completion of the Southwest Arterial in Dubuque and subsequent rerouting of US 52 in 2021, Iowa 136 was truncated again back to US 20 in Dyersville.