Since its beginnings in 1792 with the partition of the Home District into Upper Canada, the boundaries of Northumberland County have changed. With increasing settlement to the north, it shrank in 1838 with the formation of the District of Colborne, later the larger County of Peterborough. In 1974, it expanded to the west as Ontario created regional municipalities to respond to major post war growth and changes in population distribution. Prior to 1974, Port Hope and Hope Township were part of Durham County.
The maps listed below, some linked to and courtesy of John Draper's excellent Cobourg History website, illustrate the evolution from District, through the era of the United Counties to the present.
Timeline of Maps
1774-1912: The Evolution of Ontario's Boundaries (Archives Ontario page)
1788-1899 Early Districts and Counties (Archives Ontario page)
1788: Our area was in the Nassau District of the Province of Quebec.
1792: Upper Canada, showing the formation of Northumberland and Durham Counties in the Home District, formerly named the Nassau District; only township surveyed was Haldimand.
1798: District boundaries changed; Northumberland still in Home District. Hope, Cramahe and Percy Townships now had been surveyed.
1813: Northumberland. Together with Durham County, both founded in 1792, it formed the Newcastle District from 1802 to 1849. (Wikipedia). Port Hope and Hope Township were in Durham; Cobourg (previously named Amherst) in Northumberland was the District capital and county seat from 1805, except for an initial brief period when it was Newcastle which ended following the demise of the Speedy and all on board en route to the first trial in its new court house.
c1840: Northumberland Newcastle District and Northumberland County still extend well north of Rice Lake until the formation of the County of Peterborough, 1850.
1878: From 1850 to 1973, United Counties of Northumberland and Durham, administered from Cobourg.Northumberland
Durham (Courtesy of Rare Books & Special Collections, McGill University Library)
Township maps with indexes of property owners for both counties can be accessed at McGill University's "Canadian County Atlas Digital Project".
Rev Apr 26 2016: 1878 Northumberland in Google Earth
1951: from (and for larger size) Archives of Ontario Maps of Southern and Central Ontario circa 1951
2014: Ontario Road Map - indexed by municipality, from the Ontario Ministry of Transportation. Section 6 includes most of Northumberland.
Michael Stephenson has compiled quite a collection of maps covering Northumberland and Durham counties on his Ontario Genealogy website.
This is a work-in-progress that intends to overlay the historic boundaries of Newcastle District, Northumberland County and its Townships on a contemporary map.