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

Michael Stephenson has compiled quite a collection of maps covering Northumberland and Durham counties on his Ontario Genealogy website.

Boundary Map

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.