Markham , a city in the Regional Municipality of York, lies within the Greater Toronto Area of Southern Ontario, Canada. At the 2011 Canadian census it had a population of 301,709. Markham's population in 2015 was estimated at 342,000 through The Region of York population census data monitoring . The city is the fourth-largest community within the Greater Toronto Area after Toronto, Mississauga and Brampton and the largest municipality in York Region. Markham changed its status from town to city on July 1, 2012.