Milton, Ontario. Milton (2016 census population 110,128) is a town in Southern Ontario, Canada, and part of the Halton Region in the Greater Toronto Area. Between 2001 and 2011 Milton was the fastest growing municipality in Canada, with a 71.4% increase in population in 2006 and another 56.5% increase in 2011. In 2016, Milton's census population was 110,128 with an estimated growth to 228,000 by 2031.