Miss. Code Ann. § 19-1-121

Rankin County is bounded by beginning on Pearl River, in township nine, range five, east, where the old Choctaw boundary crosses said river; thence southeast with said boundary to where the same intersects the line between ranges five and six, east; thence south with said range line to the line between townships two and three, north; thence west on said township line to Pearl River; thence up said river, with its meanderings, to the beginning. The county site is Brandon.