State Trunk Highway 24 (often called Highway 24, STH 24 or WIS 24) is a state highway in the U.S. state of Wisconsin. The route a multi-lane urban arterial that serves southwestern Milwaukee County suburbs of West Allis, Greenfield and Hales Corners. The route follows Janesville Road and West Forest Home Avenue.
The route's western terminus is at the Waukesha County line in Hales Corners. West of the county line the route is signed as CTH L. The route crosses 108th street, which carries US 45 and Wisconsin Highway 100, one mile (1.6 km) east of the county line. The section of WIS 24 between the county line and 108th street is Janesville Road. The remainder of the route follows West Forest Home Avenue. East of US 45 / WIS 100, the highway turns northeast, junctioning with I-43 / I-894 in Greenfield. Further northeast the route terminates at South 27th Street, which carries WIS 241.
The original routing of WIS 24 in 1918 began in Washburn County began east of Spooner at then WIS 11 (the junction of CTH M on WIS 70). The route junctioned with the former WIS 40 (now WIS 27) and turned northward, following what is now US 63 from Hayward to south of Ashland The route followed what is now WIS 112 and terminated at WIS 13 south of Ashland. The early 1920s saw WIS 24 extended southwestward along the present day route of US 63 to Turtle Lake then to New Richmond along WIS 64 and southwest to Hudson. When US 63 was opened WIS 24 was removed from the books.
Highway 24 used to continue southwest through Waukesha, Racine and Walworth Counties to Highway 20 in East Troy, but was turned over to local control and redesignated as County Highway L in the late 1980s.
The entire route is in Milwaukee County.