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.

York was a town and the second capital of the colony of Upper Canada. It is the predecessor to the old city of Toronto (1834–1998). It was established in 1793 by Lieutenant-Governor John Graves Simcoe as a "temporary" location for the capital of Upper Canada, while he made plans to build a capital near today's London, Ontario. Simcoe renamed the location York after Prince Frederick, Duke of York and Albany, George III's second son. Simcoe gave up his plan to build a capital at London, and York became the permanent capital of Upper Canada on February 1, 1796. That year Simcoe returned to Britain and was temporarily replaced by Peter Russell.