M-189 has been largely unchanged since being designated in the 1930s, although a new bridge over the Brule River at the state line was built in 1988.

M-189 starts at the Wisconsin state line in the middle of a bridge crossing the Brule River that connects to WIS 139.

The trunkline turns north and curving to the east to run past Laurel Lake.

M-189 follows Selden Road north through the southside of the city of Iron River, continuing as 4th Street into downtown.

The trunkline ends at a junction with US 2 (Adams Street) in the middle of town.