The rivière des Mornes (in English: Mornes river) crosses the municipality of Saint-Luc-de-Bellechasse (MRC Les Etchemins Regional County Municipality), as well as Notre-Dame-Auxiliatrice-de-Buckland and Saint-Philémon, in the Bellechasse Regional County Municipality, in the administrative region of Chaudière-Appalaches, in Québec, in Canada.

The Rivière des Mornes is a tributary of the west bank of the rivière de la Fourche, which flows northward to empty onto the south bank of the rivière du Sud (Montmagny); the latter flows northwest, then northeast to the south shore of the St. Lawrence River.

The main neighboring watersheds of the Des Mornes river are: The Mornes river has its source in the township of Standon, in the municipality of Saint-Luc-de-Bellechasse, in the Les Etchemins Regional County Municipality.

From its source, the Mornes river flows over 10.6 kilometres (6.6 mi), rolling down the mountain in a deep valley, divided into the following segments: The confluence of the Mornes river is located at a place called "Les Trois-Fourches" and constitutes the head of the rivière de la Fourche.

The toponym “rivière des Mornes” was made official on February 18, 1977, at the Commission de toponymie du Québec.