Thornhill is a suburban community in the Regional Municipality of York in Ontario, Canada. It is split between the cities of Vaughan and Markham, lying along the north border of Toronto, centred on Yonge Street. Once a police village, Thornhill is now a community and postal designation. Thornhill was founded in 1794. Its first settlers on Yonge Street in Thornhill were Asa Johnson (who settled on the Vaughan side) and Nicholas Miller. Thornhill's growth since the 1960s and 1970s has been largely connected to its location bordering what is now the City of Toronto.