This watercourse flows in the municipalities of Notre-Dame-du-Rosaire, Sainte-Euphémie-sur-Rivière-du-Sud, Armagh, Saint-Raphaël, Saint-François-de-la-Rivière-du-Sud, Saint-Pierre-de-la-Rivière-du-Sud and Montmagny, in the Montmagny Regional County Municipality, in the administrative region of Chaudière-Appalaches, in the province of Quebec, in Canada.

The South River has its source in rang Saint-Thomas, in the township of D'Ashburton, in the municipality of Notre- Dame-du-Rosaire 25 km south-east of Montmagny.

This confluence which includes the bird sanctuary of Montmagny is located opposite the channel of Saint-Thomas.

Probably called "S. Antoine river" by Samuel de Champlain on his 1632 map, and "R. de S. Anthome" by Jean Boisseau, in 1643, the South river "seems to appear on the map from Jean Bourdon, drawn up around 1641, in the form of Grande Rivière du Sud.

Very stable thereafter, the toponym is part of the official designation of three municipalities drained by this course of water: Saint-Pierre-de-la-Rivière-du-Sud, Saint-François-de-la-Rivière-du-Sud and Sainte-Euphémie-sur-Rivière-du-Sud.