Iowa Highway 188 begins at a
T intersection with
Iowa Highway 3 south of
Clarksville. 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 . At four-way intersection with Butler County Road T64 and a gravel road, Iowa 188 turns to the east and becomes an east–west road for the remainder of its journey. Iowa 188 heads east for where it crosses into
Bremer County one mile (1.6 km) west of
Plainfield. One half-mile (0.8 km) into Bremer County, is a
diamond interchange with
U.S. Route 218 and
Iowa Highway 27, the Avenue of the Saints highway. In Plainfield, Iowa 188 crosses over the
Cedar River. It continues due east for , ending at
U.S. Highway 63 north of
Tripoli. ==History==