Riverhead was a small village of 20 families in 1864. It is now a town in the St. Mary's area with a population of over 400 by 1968.
In the 2021 Census of Population conducted by Statistics Canada, Riverhead had a population of living in of its total private dwellings, a change of from its 2016 population of . With a land area of , it had a population density of in 2021.