M
- Marathon
- Mississippi Mills
- Minto
- Mono
- Merrickville-Wolford
- (Hamilton) Mt Hope
- (Toronto county) Metropolitan Area Apt
- (Chatham-Kent) Mitchell's Bay
- (Lanark County) Maberly
- (Peterborough County) MacDonald Bay
- (Simcoe County) MacDonald Beach
- (District Municipality of Muskoka) Maceys Bay
- (Middlesex County) Macksville
- (Algoma) MacLennan
- (District Municipality of Muskoka) MacTier
- (Wellington County) Macton
- (Nipissing District) Madawaska
- (Parry Sound District) Maecks Subdivision
- (Huron County) Mafeking
- (Manitoulin District) Magnetic Island
- (Prince Edward County) Main Duck Island
- (United Counties of Leeds and Grenville) Mainsville
- (United Counties of Leeds and Grenville) Maitland
- (Elgin County) Malahide
- (Ottawa) Malakoff
- (Bruce County) Malcolm
- (Hastings County) Malone
- (United Counties of Leeds and Grenville) Manhard
- (Ottawa) Manion Corners
- (Manitoulin District) Manitowaning