You would do better to make your trip to the SC Archives. Chester County probate will not have wills and estates prior to about 1785, if they still have the ones that old. Most SC counties were formed about 1785 or later. Wills before that date were filed in Charleston and you would need to get them from the Archives. Most of the old county probate records have been microfilmed and are also at the archives. The counties usually have either given the old records to the archives or have them in storage. I am not familiar with how far back Chester keeps, but I would recommend that you call first to see how far back they have.