It runs north–south from WIS 77 in Upson to the Michigan border near Saxon; the route is located entirely within Iron County.

The route passes through a forested area and intersects County Trunk Highway E (CTH-E) before curving around Weber Lake.

At this point, WIS 122 briefly turns to the northwest before heading north to a junction with CTH-A.

The route then turns to the northeast and ends at the Montreal River, which marks the Michigan state line.

In 1923, WIS 122 moved to its current alignment between Upson and US 2; it was extended to the Michigan state line in 1928 or 1929.