A
- (Frontenac County) Ardoch
- (Simcoe County) Ardtrea
- (Wellington County) Ariss
- (Wellington County) Arkell
- (Lanark County) Arklan
- (Ottawa) Arlington Woods
- (Thunder Bay District) Armstrong
- (Wellington County) Armstrong Mills
- (Lanark County) Armstrongs Corners
- (Thunder Bay District) Armstrong Station
- (Grey County) Arnott
- (Bruce County) Arranvale
- (Wellington County) Arthur
- (Oxford County) Arthur's Corners
- (Middlesex County) Arva
- (Peterborough County) Ashby Mill
- (Lanark County) Ashton Station
- (Lennox and Addington County) Asselstine
- (Peterborough County) Assumption
- (Nipissing District) Astorville
- (Simcoe County) Atherley
- (Simcoe County) Athlone
- (Lanark County) Atironto
- (Regional Municipality of Niagara) Attercliffe
- (Huron County) Auburn
- (Renfrew County) Augsburg
- (Middlesex County) Avon
- (Perth County) Avonbank
- (Lambton County) Avonry
- (Perth County) Avonton