State Route 120 (SR 120) is a north–south secondary state highway located entirely in Stewart County in northwestern Middle Tennessee.

[2] SR 120 starts at a junction with US 79/SR 76 near Big Rock.

The highway goes north for a short distance before turning west to pass along the north side of Big Rock.

SR 120 then winds its way southwest before turning north again to pass through Bumpus Mills before coming to an end at the Kentucky state line, where it continues as Kentucky Route 139 (KY 139) upon entry into Trigg County, Kentucky.

The entire route is in Stewart County.