Toronto's First Post Office (or Fourth York Post Office) is the oldest purpose-built post office in Toronto, Ontario, Canada, and the only surviving example of a post office that functioned as a department of the British Royal Mail.
The building was built between 1833 to 1834, with construction commencing before York became the City of Toronto. Therefore, the post office is known both as the "Fourth York Post Office" (as there had been three prior post offices in the settlement) and the "First Toronto Post Office" (as it was the first post office to serve the newly incorporated city). The building served as a post office until 1839. It was altered last in 1876. Located at 260 Adelaide Street East, the building now houses a museum and a full-service post office, run by the Town of York Historical Society.