Toronto's First Post Office is a historic post office in Toronto, Ontario. 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 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.

A post office is a public facility and a retailer that provides mail services, such as accepting letters and parcels, providing post office boxes, and selling postage stamps, packaging, and stationery. Post offices may offer additional services, which vary by country. These include providing and accepting government forms, and processing government services and fees. The chief administrator of a post office is called a postmaster.