The United Counties of Northumberland and Durham was a
historic county in the
Canadian province
Canada has ten provinces and three territories that are sub-national administrative divisions under the jurisdiction of the Constitution of Canada, Canadian Constitution. In the 1867 Canadian Confederation, three provinces of British North Amer ...
of
Ontario
Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...
. The two counties were originally combined in the
District of Newcastle formed in 1802, and continued as united counties from 1850 until January 1, 1974, when portions of
Durham County were amalgamated with adjacent
Ontario County to form the
Regional Municipality of Durham
The Regional Municipality of Durham (), informally referred to as Durham Region, is a regional municipality in Southern Ontario, Canada. Located east of Toronto and the Regional Municipality of York, it forms the east end of the Greater Toronto A ...
.
Manvers Township went to
Victoria County and what is now
Cavan-Monaghan went to
Peterborough County
Peterborough County is a county and census division located in Southern Ontario, Canada. The county seat is the City of Peterborough, which is independent of the county.
The southern section of the county is mix of agriculture, urban and lakef ...
. What is now
Port Hope remained in the area which was continued as
Northumberland County, while Durham County was restructured into Durham Region.
Former counties in Ontario
Populated places disestablished in 1974
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