The line from Sumter to Darlington was built as part of the Charleston, Sumter & Northern in 1890. It was hoped that the CS&N would become part of the SAL and its main line into Georgia and north Florida. The ACL bought the CS&N in 1895 through subsidiary Charleston & Northern and assigned this section to the Manchester & Augusta, which became the ACL after 1900.
This section was abandoned in the 1950s. Sections of the ROW can still be made out in Sumter, along the Lynches River next to US401, and in Lamar. The section from Darlington to Marlboro (south of Bennettsville) was also part of the old CS&N, and connected in Bennettsville with another ACL line from the A-line south of Fayetteville through Red Springs and Maxton, NC, through McColl, SC and into Bennettsville. The section from McColl to Bennettsville to Marlboro remains in service as the Pee Dee RR. A few pieces of the old ACL line from McColl to south of Fayetteville remain in service. The old CS&N line from Bennettsville to Gibson, NC was shared with the Rockingham Railroad in the ACL era, but has now been abandoned N of Breeden near Bennettsville.
The section from Darlington to Marlboro was abandoned in pieces, with the last section being abandoned in the late 1970s by Seaboard Coast Line. The ROW can still be made out in some places, particularly in Darlington.
See also an account of the last trip on the Sumter to Darlington Line