Brant Lake South is a census-designated place (CDP) in Lake County, South Dakota, United States.

It is bordered to the north by the town of Brant Lake and to the south by the unincorporated community of Chester.

Madison, the county seat, is 13 miles (21 km) to the northwest.

According to the U.S. Census Bureau, the Brant Lake South CDP has an area of 1.0 square mile (2.7 km2), of which 0.54 square miles (1.4 km2) are land and 0.50 square miles (1.3 km2), comprising the southeastern portion of Brant Lake, are water.

[4] Skunk Creek, the outlet of Brant Lake, passes through the southwest corner of the CDP and flows south to the Big Sioux River at Sioux Falls.