In the 2021 Census of Population conducted by Statistics Canada, Saint-Sébastien had a population of 674 living in 301 of its 329 total private dwellings, a change of 2.6% from its 2016 population of 657. With a land area of 91.95 km2 (35.50 sq mi), it had a population density of 7.3/km2 (19.0/sq mi) in 2021.[4]