Kentucky Route 121 (KY 121) is a 69.383-mile-long (111.661 km) state highway in Kentucky.

It runs from State Route 119 (SR 119) at the Kentucky–Tennessee state line southeast of New Concord to U.S. Route 51 (US 51) and US 62 in Wickliffe via Murray and Mayfield.

It runs through downtown, while KY 121 uses a bypass to the east and north.

It runs concurrent with U.S. Route 45 for its final two miles.

The entire route is in Graves County.