Manitoulin Island, 2765 km2, the largest island in the world located in a lake, is part of an archipelago at the top of Lake Lake Huron straddling the Ontario-Michigan border. Its northern shore encloses the North Channel, which leads to the St Mary's River at Sault Ste Marie. An extension of the Niagara Peninsula, Manitoulin Island has an irregular, rocky shoreline and many interior lakes.

In the 17th century, it was part of the territory occupied by the Odawa, who called it Mnidoo Mnis, meaning "island of the Great Spirit." The Odawa believed that Mnidoo or Manitou dwelt on the island. Jesuit missionaries arrived in 1648, but their mission was short-lived. The island was sporadically inhabited until the 1830s when it became the centre of Aboriginal administration for northern Ontario. First Nations from across the region were settled here and others visited to receive their annual presents from the British government. In 1862, the provincial government purchased most of the island from the First Nations, except for the most northeastern section. By this time, settlers were arriving to clear farms. The island's First Nations now live on small reserves, including Wikwemikong, the unceded reserve of the Odawa and Ojibwa.

Though the island is fertile only in spots, farming has always been a major economic activity. Turkey production thrived after 1920 and by 1930, the island was one of the most important sheep-rearing areas in Ontario. Logging dates from the 1860s and commercial fishing for whitefish and trout was also an economic mainstay; however, both these industries have declined.

Since the 1920s, the island has become a popular outdoor recreation area, and tourism and agriculture are now the principal activities. Little Current, within the town of Northeastern Manitoulin and the Islands, and Gore Bay are the main populated centres. Little Current is linked to the mainland by road. The railway reached Little Current in 1913 but the line was abandoned in 1980. The swing bridge built for the railway remains for vehicle traffic. A ferry runs for much of the year from South Baymouth to Tobermory on the northern tip of the Bruce Peninsula.