Cockburn Island is an island in the Canadian province of Ontario, located in the Manitoulin District. It is separated from the westernmost point of Manitoulin Island by the Mississagi Strait, and from Michigan's Drummond Island by the False Detour Channel.
Most of the island is incorporated as the municipal township of Cockburn Island, which had a permanent population of ten in the 2006 Canadian census. In the 2001 census the island's population had been reported as zero, due to Statistics Canada's counting method of rounding off population figures for communities of smaller than 15 people. It is the least populated incorporated municipality in Canada, and township offices are located on the mainland in Thessalon in the district of Algoma.
At one time, the island had a population of several hundred people, centred primarily on fishing operations at Tolsmaville, which was once also known as Port Cockburn, and logging operations at Ricketts Harbour. Tolsmaville continues to be the primary settlement on the island, operating as the hub of the island's summer tourist economy, even though some references incorrectly describe it as a wholly abandoned ghost town.
A small portion of the island is taken up by the Cockburn Island 19 Indian reserve, which has no permanent population — this is a heritage land belonging to a First Nation whose primary community is located on Manitoulin Island.
In addition to the summer recreational economy, a modest logging industry continues to operate on the island.
The island is not connected to either Manitoulin or Drummond Islands, or to the mainland, by bridge or ferry service. The municipality maintains a marina at Tolsmaville for private boats and float planes, and a small grass airstrip located west of Tolsmaville provides a landing area for private planes.
Historically, when the island had a larger permanent resident population, it received ferry service, most notably from the MS Norgoma. The island's population declined rapidly when this service was discontinued in 1963.