WIS 23 passes through rolling hills in the town of Willow Springs and enters Iowa County 10 miles (16 km) north of the city.

WIS 39 joins the route one mile (1.6 km) southeast of the city, and turns west off in the downtown area.

[3] WIS 23 passes through Spring Green upon entering Sauk County and crosses US 14 just north of the village.

The highway passes through Mirror Lake State Park just prior to entering the village via Monroe Avenue.

The highway concurrency of 23 and 49 enters Fond du Lac County two miles (3 km) east of Green Lake.

As the highway enters Fond du Lac, it junctions with I-41 and becomes Johnson St., the main east–west thoroughfare through the city.

The freeway segment ends a mile east of Interstate 43 at North 25th Street, with an exit at Taylor Drive.

[17] Erie Avenue continues undesignated for about .9 of a mile east, until coming to an end at a cul-de-sac a block west of Lake Michigan, overlooking Broughton Drive.

Proposals were considered that would have rerouted WIS 23 around Lake Delton by following CTH-H from Reedsburg directly to Wisconsin Dells, but were never pursued due to pressure from the village of Lake Delton and the area's tourist attractions like hotels and resorts fearing lost business from the re-routing.

[1] The Wisconsin Department of Transportation (WisDOT) had made WIS 23 between Fond du Lac and Sheboygan a priority state corridor in its highway planning, studying the expansion of WIS 23 from Fond du Lac to Plymouth to a four-lane expressway, as the rural two-lane portion between Mount Calvary and Greenbush towards the county line, along with the two-lane narrowing just outside of Fond du Lac on a steep grade into the Kettle Moraine State Forest area, was a stretch where various crashes with casualties occurred.

A draft environmental impact statement was presented in 2004 and the bypass route following the existing alignment was chosen in 2005.

[21] Construction[22] of the expansion was scheduled to begin in 2015, but was delayed by a lawsuit by an environmental group which prevented delegation of federal funds until resolved, along with overall political issues involving the state transportation budget.