From Iowa 3, Iowa 188 heads north where it crosses the Shell Rock River and forms the eastern boundary of Heery Woods State Park.

It passes through Clarksville and continues north for 4 miles (6.4 km).

It continues due east for 10 miles (16 km), ending at U.S. Highway 63 north of Tripoli.

Iowa 188 was designated in 1945 as a 10-mile-long (16 km) route which connected US 218 at Plainfield to US 63.

That year the section of highway between Clarksville and Plainfield was turned over to Butler County officials and the section south of Clarksville became Iowa 122.