Finally, it serves southeastern Wisconsin, connecting Madison with Fort Atkinson, Whitewater, Elkhorn, and Lake Geneva.

Between Hudson and west of Warrens, the road closely parallels the former main line of the Chicago, St. Paul, Minneapolis and Omaha Railway, now operated by Union Pacific Railroad.

[3] The highways meet an interchange with I-94, then split one half of a mile (0.80 km) east in Elk Mound at the junction with WIS 40.

[8] The highway crosses I-94 (with no access) south of Kirby and junctions with WIS 21 on the north side of Tomah at an interchange with the Interstate.

The routes trek eastward and pass through Lyndon Station, where Rocky Arbor State Park is located.

Olympus Water & Theme Park, Wilderness Territory, and Tommy Bartlett Show.

Just northwest of Middleton, the route becomes a freeway as it enters the Madison area along the West Beltline Highway.

During the four-way concurrency, the freeway passes the interchange of Seminole Highway (only accessible from the westbound side), the University of Wisconsin–Madison Arboretum, and the interchanges of Todd Drive, Fish Hatchery Road (CTH-D), and Park Street, where US 14 leaves to go south and US 151 north into downtown Madison.

[16] US 12 and US 18 continue as an expressway east of the Interstates, junctioning with WIS 73 in Deerfield and splitting, with US 12 turning southeast into Jefferson County in Cambridge.

WIS 89 joins US 12 as the route turns southward to approach Whitewater, bypassing the city to the south into Walworth County.

The highway turns south into Genoa City, where the freeway ends and US 12 follows the crossroad into Illinois.

The entire route was originally signed as WIS 12 in 1917 prior to the creation of the U.S. Numbered Highway System in 1926.

From Black River Falls, WIS 12 continued south to Shamrock and turned east to follow CTH-O to Millston.

Widening US 12 between Middleton and Sauk City was completed in 2005, but local opposition prevented most of the remaining route north of that point to Lake Delton from being constructed.