In 2016, Milton's census population was 110,128 with an estimated growth to 228,000 by 2031. It remained the fastest growing community in Ontario but was deemed to be the sixth fastest growing in Canada at that time.

In the 2021 Census of Population conducted by Statistics Canada, Milton had a population of 132,979 living in 40,038 of its 41,000 total private dwellings, a change of 20.7% from its 2016 population of 110,128. With a land area of 363.83 km2 (140.48 sq mi), it had a population density of 365.5/km2 (946.6/sq mi) in 2021.

An October 2019 report stated that the average household income was $111,875, that the unemployment rate was 5.7%, and that the crime rate per 100,000 residents was low, at 2,133.