It was based on the western portion of Halton County, termed a riding.

[2] Halton County had been an electoral district in the Upper Canada Parliament, but it was changed by the Union Act.

[4] In 1841, the County of Halton was split into two ridings for the new Parliament of the Province of Canada.

[8] It was succeeded by electoral districts of the same name in the House of Commons of Canada[9] and the Legislative Assembly of Ontario.

This article incorporates text from this source, which is in the public domain: Union Act, 1840, 3 & 4 Vict.