 As the highway enters Fond du Lac, it junctions with I-41 and becomes Johnson St., the main east–west thoroughfare through the city.WIS 23 crosses US 45 in the city center and US 151 on the east side.After a twelve-mile (19 km) rural stretch from Fond du Lac, WIS 23 enters Sheboygan County The route passes near Greenbush about four miles (6 km) into the county, then becomes a freeway about two miles (3 km) northwest of Plymouth.