S.C. Code § 4-5-220
The General Assembly upon receipt of the certified returns shall as soon as practicable alter the county line or lines in accordance with the request or petition if two-thirds of the qualified electors voting or otherwise indicating their preference, under Section 4-5-170(B), on the question in the area to be transferred vote or otherwise indicate, under Section 4-5-170(B), in favor of the transfer and if a majority of the qualified electors voting in the county to which the transfer is proposed or the members of the county governing boards, under Section 4-5-170(B), vote in favor of the transfer, provided that all the constitutional requirements for the alteration of county lines have been complied with, all of which must be determined by the General Assembly. The annexation must then become effective.
S.C. Code § 4-5-220