Durham County was composed of the townships of Cartwright, Manvers, Cavan, Darlington, Clarke and Hope, and portions of what is now Peterborough County. 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. About half of Durham County was merged with Ontario County to create the Regional Municipality of Durham, thus Ontario County is no longer on maps. The township of Manvers was transferred to Victoria County, Cavan was transferred to Peterborough County and Hope was transferred to Northumberland County. 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 the Township of Scugog.