S.C. Code § 4-3-310
Horry County is bounded as follows: by a line originating at the point where the boundary line between South Carolina and North Carolina intersects the center line of the Lumber River; thence southwestward following the center line of the Lumber River to its intersection with the center line of the Little Pee Dee River; thence southwestward and southeastward following the center line of the Little Pee Dee River to its intersection with the center line of the Great Pee Dee River; thence southeastward following the center line of the Great Pee Dee River to its intersection with the center line of Bull Creek; thence southeastward following the center line of Bull Creek to its intersection with the center line of the Waccamaw River; thence southward following the center line of the Waccamaw River to a point at latitude 33° 34' 22.623" N, longitude 79° 06' 03.848" W (North American Datum 1983) in the Waccamaw River; thence eastward following a straight line to a point at latitude 33° 34' 21.602" N, longitude 79° 00' 06.564" W (North American Datum 1983) on the seashore; thence on a true azimuth of 126° (bearing of S 54° E) to the Territorial Sea boundary; thence northeastward following the Territorial Sea boundary to its intersection with the seaward boundary between South Carolina and North Carolina; thence northwestward following the seaward boundary between South Carolina and North Carolina on a line as described by monuments located at latitude 33° 51' 50.7214" N, longitude 78° 33' 22.9448" W (NC-SC Granite Marker #2); latitude 33° 51' 36.4626" N, longitude 78° 33' 06.1937" W (NC-SC Granite Marker #1); and latitude 33° 51' 07.8792" N, longitude 78° 32' 32.6210" W (Bird Island-NC-SC Boundary 1977) (North American Datum 1927); thence northwestward following the boundary line between South Carolina and North Carolina to its intersection with the center line of the Lumber River, the point of origin.
S.C. Code § 4-3-310