Created in 1792, at its largest size, it encompassed the area that presently comprises the City of Toronto, the regional municipalities of Halton, Peel, and York as well as portions of Regional Municipality of Durham and the City of Hamilton.

In 1953, York County was split again, with the area south of Steeles Avenue forming the Municipality of Metropolitan Toronto.

York County was created on 16 June 1792[1] and was part of the jurisdiction of the Home District of Upper Canada.

The town of York, later incorporated as the City of Toronto in 1834, served as the initial seat for the county.

After the creation of Metropolitan Toronto in 1953, the seat of government for York County was moved to Newmarket.

[3])After the Battle of York, the county officials and legislative assembly met at the home of Major Alexander Montgomery Jr., located on north side of Richmond Street between Yonge and Victoria Streets (now Confederation Life Building).