Tennessee State Route 51State Route 51 is a rural secondary north–south state highway that traverses the northwestern portion of Clay [County, Tennessee|Clay County] in Middle Tennessee. It is long.Route descriptionSR 51 begins at a Y-intersection with Tennessee [State Route 52|SR 52] at Moss. Its northern end is located at the Kentucky state line where it becomes Kentucky Route 163 upon entry into Monroe County, Kentucky. SR 51 is known as “Tompkinsville Highway” for its entire length.Major intersections