In the 2021 Census of Population conducted by Statistics Canada, Saint-Nazaire-de-Dorchester had a population of  living in  of its  total private dwellings, a change of  from its 2016 population of .
In the 2021 Census of Population conducted by Statistics Canada, the population of Saint-Nazaire-de-Dorchester was , residing in some of its total private dwellings, an increase from its 2016 population.