State Trunk Highway 121 (often called Highway 121, STH-121 or WIS 121) is a 45.07-mile (72.53 km) state highway in Buffalo, Trempealeau, and Jackson counties in the west-central area of the US state of Wisconsin that runs east–west from Gilmanton to near Alma Center.

Starting at WIS 88 in Gilmanton, WIS 121 starts to travel eastward, passing through Lookout and Russell. Then, WIS 121 turns south along WIS 93. In Independence, WIS 121 leaves eastward away from WIS 93. Then, in Whitehall, WIS 121 begins to run concurrently with US Highway 53 (US 53). They then pass through Coral City. Then, in Pigeon Falls, WIS 121 branches eastward, passing through York and Northfield. In Northfield, it then meets Interstate 94 (I-94) at a diamond interchange. Continuing further east, WIS 121 then ends at WIS 95 west of Alma Center.

This section is missing mileposts for junctions. Please help by adding them.

County	Location	mi	km	Destinations	Notes
Buffalo	Gilmanton			WIS 88 – Mondovi, Fountain City
Trempealeau	Town of Burnside			WIS 93 north – Eleva	Western end of WIS 93 concurrency
	Independence			WIS 93 south – Arcadia	Eastern end of WIS 93 concurrency
	Whitehall			US 53 south – Ettrick	Western end of US 53 concurrency
	Pigeon Falls			US 53 north – Osseo	Eastern end of US 53 concurrency
Jackson	Northfield			I-94 – Eau Claire, Madison
	Town of Garden Valley			WIS 95 – Alma Center, Merrillan, Hixton
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

• U.S. Roads portal

• Media related to Wisconsin Highway 121 at Wikimedia Commons