Manitoulin District is a district in Northeastern Ontario within the Canadian province of Ontario. It was created in 1888 from part of the Algoma District. The district seat is in Gore Bay. It comprises Manitoulin Island primarily, as well as a number of smaller islands surrounding it, such as Barrie, Cockburn, and Great La Cloche islands. Previously it included the municipality of Killarney on the mainland, until this was transferred to Sudbury District in the late 1990s. Subsequently, more mainland portions were added to Killarney and these, together with Unorganized Mainland Manitoulin District, were also transferred to Sudbury District in 2006, about 1,600 square kilometres (600 sq mi) in all.