Toronto's First Post Office (also known as the Fourth York Post Office National Historic Site of Canada) is a historic post office in Toronto, Ontario, Canada. It is the oldest purpose-built post office in Canada that functioned as a department of the British Royal Mail, and the only surviving example. After its initial use as a post office, it became part of a Roman Catholic boys' school (De La Salle College) and later a cold storage building. Located at 260 Adelaide Street East in downtown Toronto, the building now houses a museum and a full-service post office, run by the Town of York Historical Society.