High Quality Content by WIKIPEDIA articles! The Regional Municipality of Durham, informally referred to as Durham Region, is a regional municipality located in Southern Ontario east of Toronto, Ontario. It has an area of approximately 2,500 square kilometres. Durham Region is considered part of the Greater Toronto Area, with the communities of Oshawa, Whitby, and Clarington making up the Oshawa Census Metropolitan Area. The regional government is headquartered in Whitby.