State Trunk Highway 128 (often called Highway 128, STH-128 or WIS 128) is a 27.04 miles (43.52 km) state highway in Pierce and St. Croix counties in Wisconsin, United States. It runs in north–south in northwest Wisconsin from near Elmwood to Forest.

The highway begins at an intersection with WIS 72 and runs north from it, following the Eau Galle River until its intersection with County Trunk Highway B (CTH-B), from which it continues north. It passes through intersections with WIS 29 and CTH-N and an interchange with Interstate 94 (I-94) before intersecting with US Highway 12 (US 12) near Hersey and Wilson. It then continues north before curving eastward to meet WIS 170 in Glenwood City. From there it runs north until it terminates at WIS 64.

Initially, in 1923, WIS 128 was established roughly along part of its present-day route and present-day CTH-B from WIS 51 (now WIS 72) in Elmwood to WIS 116 (now WIS 29) in Spring Valley. Then, in 1934, WIS 128 extended northward to WIS 79 in Glenwood, superseding CTH-A in the process. In 1947, WIS 79 moved off from Glenwood and instead served Connorsville. As a result, WIS 170 extended westward towards Glenwood while WIS 128 extended northward towards WIS 64. By 1994, WIS 128 moved eastward onto the existing bypass of Spring Valley, superseding CTH-T. As a result, CTH-B was established to follow along part of the former alignment.

County	Location	mi	km	Destinations	Notes
Pierce	Elmwood–Spring Lake line	0.0	0.0	WIS 72 – Ellsworth, Downsville
St. Croix	Cady	7.2	11.6	WIS 29 – Spring Valley, Menomonie
		11.5	18.5	I-94 – Hudson, Menomonie	Interchange
	Springfield	13.0	20.9	US 12 – Woodville, Wilson
	Glenwood City	20.9	33.6	WIS 170 east – Downing, Boyceville
	Forest	27.1	43.6	WIS 64 / CTH-P north – New Richmond, Connorsville
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

• U.S. Roads portal

• Media related to Wisconsin Highway 128 at Wikimedia Commons