In the 2021 Canadian census conducted by Statistics Canada, Oakville had a population of 213,759 living in 73,558 of its 76,179 total private dwellings, a change of 10.3% from its 2016 population of 193,832. With a land area of 138.94 km2 (53.65 sq mi), it had a population density of 1,538.5/km2 (3,984.7/sq mi) in 2021.

According to the 2021 census, the median age in the town is 41.6 years. 18% of the population is under 15 years of age, 66.3% is between 15 and 64 years, and 15.7% is 65 and over.

In 2016, immigrants made up 35.9% of the population. The top 10 places of birth of the immigrant population were the United Kingdom (11%), China (9.3%), India (7.6%), Pakistan (4.2%), Poland (3.8%), Philippines (3.7%), the United States (3.4%), Portugal (3.3%), Egypt (3.1%), and South Korea (2.9%).