State Trunk Highway 33 (often called Highway 33, STH 33 or WIS 33) is a Wisconsin state highway running east–west across central Wisconsin. It is 200.84 miles (323.22 km) in length.

The eastern terminus of Highway 33 is one mile (1.6 km) west of Lake Michigan where it intersects with Highway 32 in downtown Port Washington, Wisconsin. The western terminus is 300 feet (91 m) east of the Mississippi River where it intersects with U.S. Highway 14 just south of downtown La Crosse, Wisconsin.

Prior to European settlement, the foot trail from Port Washington to Horicon was the most traveled of seven trails that met in Horicon Marsh. A road was constructed to provide access from Lake Michigan to the fertile hunting grounds of the marsh, to provide food for the crews of ships on the lake. It is one of the oldest roads in Wisconsin.[citation needed]