State Trunk Highway 21 (often called Highway 21, STH 21 or WIS 21) is a state highway in the U.S. state of Wisconsin. It runs east–west across the center of the state between Sparta, Wisconsin and Oshkosh. The route often serves as a direct route for travelers between Appleton and Oshkosh to Tomah, and La Crosse It is a two-lane surface road for nearly all of its length, with the exception of a few urban arterials of four or more lanes. The section of WIS 21 between Fort McCoy and I-94 in Tomah is classified as a "Major STRAHNET Connector." while the route past I-94 is classified as a "Non-Interstate STRAHNET Route"