M
- (District Municipality of Muskoka) Mariebianca Island
- (Comtés unis de Prescott et Russell) Marionville
- (Simcoe County) Mariposa Beach
- (Grey County) Marmion
- (Hastings County) Marmora
- (Huron County) Marnoch
- (Ottawa) Marshall Bay
- (Durham) Marsh Hill
- (Dufferin County) Marsville
- (Lambton County) Marthaville
- (Simcoe County) Martin Farm
- (Renfrew County) Martins Corner
- (Ottawa) Martins Corners
- (Hastings County) Martins Landing
- (Simcoe County) Martinville
- (Simcoe County) Martyrs Shrine
- (Comtés unis de Prescott et Russell) Marvelville
- (Hastings County) Marysville
- (Lennox and Addington County) Massanoga
- (Sudbury) Massey
- (Timiskaming District) Matachewan
- (Peterborough County) Mathers Corners
- (Cochrane District) Matheson
- (Cochrane District) Mattice
- (Grey County) Maxwell
- (Middlesex County) Mayfair
- (Renfrew County) Mayhews Landing
- (United Counties of Leeds and Grenville) Maynard
- (Huron County) Mayne Corners
- (Hastings County) Maynooth