South Twin Lake having about 3,200 acres (13 km²) is wholly within Penobscot County, Maine. It is about 6 miles (10 km) west of Millinocket, Maine and is part of the Pemadumcook Chain of Lakes. The lake is centered at (45°37.25′N68°51′W) and has spillway elevation 492 feet (150 m) above sea level.