Durham County was created in 1792. It was composed of the townships of Cartwright, Manvers, Cavan, Darlington, Clarke and Hope, and portions of what is now Peterborough County, created in 1838. It was united administratively with Northumberland County as the United Counties of Northumberland and Durham from 1800 until Durham County was dissolved on January 1, 1974.
Effective January 1, 1974, about half of Durham County was merged with Ontario County to create the Regional Municipality of Durham. The township of Manvers was transferred to Victoria County, which is now the city of Kawartha Lakes, Cavan was transferred to Peterborough County, where it is now part of Cavan-Monaghan, and Hope was transferred to Northumberland County, where it is now part of the town of Port Hope.
The townships of Darlington and Clarke were amalgamated with the Town of Bowmanville and the Village of Newcastle as the Town of Newcastle, and the township of Cartwright was combined with the Ontario County townships of Scugog and Reach to create a new Township of Scugog. In 1993, Newcastle was renamed Clarington.
Source: Province of Ontario -- A History 1615 to 1927 by Jesse Edgar Middletwon & Fred Landon, copyright 1927, Dominion Publishing Company, Toronto. Source: The Trail Through The Bush - A brief history of Manvers Township. By Sherrell Branton Leetooze. copyright 1998 L.M-J Associates.