State Route 51 (SR 51) is a rural secondary north–south state highway that traverses the northwestern portion of Clay County in Middle Tennessee.

SR 51 begins at a Y-intersection with SR 52 (Clay County Highway) at Moss.

Its northern end is located at the Kentucky state line where it becomes Kentucky Route 163 (KY 163) upon entry into Monroe County, Kentucky.

[2][3] SR 51 is known as “Tompkinsville Highway” for its entire length.

[4][5] The entire route is in Clay County.