1885 Map of York County, Ontario

York County is a historic county in Upper Canada, Canada West, and the Canadian province of Ontario.

York County was created in 1792 and was part of the jurisdiction of Home District of Upper Canada. It originally comprised all of what is now York Region, Peel Region, Halton Region, Toronto, parts of the current Durham Regional Municipality and the current city of Hamilton.

In 1816, Wentworth County and Halton County were created from York County. In 1851, Ontario County and Peel County were separated from York.

In 1953, Metropolitan Toronto was separated from York County. At this time, the townships of Etobicoke, York and Scarboro (now Scarborough) seceded from York County, and the county office was moved to Newmarket from Toronto (The York County Court house in Toronto is the only reminder of the former county seat in Toronto).

In 1971, the remaining portion of York County was replaced by the York Regional Municipality.