The estimated 2024 population of Sainte-Marthe-sur-le-Lac is 20,909. The population of Sainte-Marthe-sur-le-Lac was recorded at 19,797 in the 2021 Canadian Census, and was recorded at 18,074 in the 2016 census. This is a change in population of 1,723, which is an annual growth rate of 1.84%.