York County is a historic county in Upper Canada, Canada West, and the Canadian province of Ontario. It was organized by the Upper Canada administration from the lands of the Toronto Purchase and others.

The Toronto Purchase was the sale of lands in the Toronto area from the Mississaugas of New Credit to the British crown. An initial, disputed, agreement was made in 1787, in exchange for various items. The agreement was revisited in 1805, intended to clarify the area purchased. The agreement remained in dispute for over 200 years until 2010, when a settlement for the land was made between the Government of Canada and the Mississaugas for the land and other lands in the area.