S.C. Code Ann. § 25-1-1900

Whenever any portion of the National Guard or militia is employed in aid of the civil authority, the Governor, if in his judgment the maintenance of law and order will thereby be promoted, may by proclamation declare the county or city in which the troops are serving or any specified portion thereof to be in a state of insurrection, rebellion, tumult, riot, resistance to law or process or breach of the peace.