Manitoulin was a provincial electoral district in the Canadian province of Ontario. It was located in Northeastern Ontario and encompassed Manitoulin Island and surrounding parts of the mainland in the Sudbury District.
The riding was created in 1908 from parts of the former Algoma provincial electoral district. It was established to provide dedicated representation for the growing population of Manitoulin Island and the adjacent mainland communities. Its boundaries remained relatively stable throughout its existence, though minor adjustments would have occurred during redistribution processes to account for population shifts.
Manitoulin was characterized by its mixed demographic, including a significant presence of First Nations communities, and a predominantly rural and resource-based economy. Like many northern Ontario ridings, it often elected representatives from the Ontario Liberal Party or the Ontario New Democratic Party, reflecting the region's political leanings.
The electoral district ceased to exist as a standalone entity in 1999. As part of a province-wide redistribution of electoral boundaries to align provincial ridings more closely with federal ones, Manitoulin was merged with parts of the Algoma riding to form the new provincial electoral district of Algoma—Manitoulin. This larger riding continues to represent the geographic area that Manitoulin once covered.