South Carolina Highway 109 (SC 109) is a 14.520-mile (23.368 km) primary state highway in the U.S. state of South Carolina.

SC 109 is a two-lane rural highway that traverses from SC 145 through Ruby and Mount Croghan, to the North Carolina state line.

[2] SC 109 was established in either 1937 or 1938 as a new primary route from SC 9 in Mount Croghan to the North Carolina state line.

In 1941 or 1942, SC 109 was extended south again to U.S. Route 15 (US 15) in Hartsville; there was also a four-mile (6.4 km) separate piece connecting SC 155 to US 52.

In 1948, SC 109 moved back to its current southern terminus at SC 145; both the former extension and separate piece were downgraded to secondary roads.