WIS 188 starts in rural Dane County across the Wisconsin River from Sauk City.

The highway runs northward through farm fields on the east side of the river, crosses into Columbia County, and heads to an intersection with WIS 60 east of Prairie du Sac.

The two highways run concurrently to the northeast for about 1.5 miles (2.4 km) before WIS 188 separates and turns northward again.

Near Lake Wisconsin, the highway turns east and then back north before sticking to an eastward course along a bend in the river.

[1] Around 1942, the routing of WIS 78 was shifted to the east side of the Wisconsin River between Sauk City and the Merrimac Ferry.