The Duncan River is a tributary of the rivière le Renne, which flows in the municipalities of Saint-Germain-de-Grantham (a sector of Drummondville), Saint-Nazaire-d'Acton, Saint-Théodore-d'Acton and Upton, in the Acton Regional County Municipality (MRC), in Montérégie, on the South Shore of the Saint Lawrence River, in Quebec, Canada.

The main neighboring hydrographic slopes of the Duncan River are: The Duncan River draws its sources to the south of a marsh area (length of 1.2 km [0.75 mi]) in the south-eastern part of the territory of Saint-Germain-de-Grantham, near the limit of the municipality of Wickham.

The mouth of the Duncan River is located 4.6 km (2.9 mi) northeast of the village of Upton, 3.2 km (2.0 mi) north of route 116 and 3.7 km (2.3 mi) upstream from the mouth of the rivière le Renne.

[1] In the past, this watercourse was called the “Saint-Nazaire river”.

The toponym “Duncan River” was officially registered on July 9, 1980, at the Commission de toponymie du Québec.