Durham electoral district was based on Durham County, on the north shore of Lake Ontario, in Canada West (now the province of Ontario), east of what is now Toronto.

[2] Durham County had been an electoral district in the Legislative Assembly of Upper Canada,[3] and its boundaries were not altered by the Act.

Those boundaries had been initially been set by the first Lieutenant Governor of Upper Canada, John Graves Simcoe, in 1792: The boundaries were further defined by a statute of Upper Canada in 1798, and modified by an additional statute in 1834: In 1834, the townships of Verulam, Fenelon and Eldon were added to Durham County.

[6] Since Durham was not changed by the Union Act, those boundaries continued to be used for the new electoral district.

[11] This article incorporates text from this source, which is in the public domain: Proclamation, Lieutenant Governor John Graves Simcoe, July 16, 1792 This article incorporates text from this source, which is in the public domain: An act for the Better Division of this Province, SUC 1798, c. 5.