If you are searching for your ancestors in South Carolina, and they were of Irish origin, the following counties are where to look. Most Irish were from Northern Ireland and landed in Philadelphia and Charleston. Thus, you know where to begin your research. The families did not remain in Philadelphia for long, and they traveled by wagon, pack-horse, or foot through the Kiltatinny Valley, west of the Susquehanna and Potomac Rivers, and southward through the Shenandoah Valley.
It is presumed that those families who landed in Charleston, South Carolina, settled in the counties of Charleston, Chester, Lancaster, Laurens, and York.
https://southcarolinapioneers.net/country/charleston/
https://southcarolinapioneers.net/country/chester/
https://southcarolinapioneers.net/country/laurens-2/