Marion County is bounded as follows: on the north by Dillon County; on the west by the Great Pee Dee River; thence down the Great Pee Dee River, which divides it from Florence, Williamsburg and Georgetown Counties, to the mouth of the Little Pee Dee River; thence up the Little Pee Dee and Lumber Rivers, separating it on the east from Horry County, to the line of Dillon County on the Little Pee Dee River.
Marion County
S.C. Code Ann. § 4-3-380, under Title 4, Chapter 3.
S.C. Code Ann. § 4-3-380