Marlboro County Probate Office and Court House have good records and the people there are very helpful. There is also the Marlborough Historical Society and Historical Museum which may be of help. None of their information is on line that I know of. I would suggest you contact both about their hours of operation.
Much would depend on how long your ancestor was in the area and if he owned land there.
By all means visit the South Carolina State Archives in Columbia. They, too, are very helpful and have lots of information.