In the 2021 Census of Population conducted by Statistics Canada, Saint-Marcellin had a population of 397 living in 213 of its 324 total private dwellings, a change of 12.5% from its 2016 population of 353. With a land area of 117.19 km2 (45.25 sq mi), it had a population density of 3.4/km2 (8.8/sq mi) in 2021.[4]