King's Highway 66, commonly referred to as Highway 66, is a provincially-maintained highway in the Canadian province of Ontario. Located in the Timiskaming District, the highway begins at Matachewan near a junction with Highway 65. It extends eastward for 107.0 kilometres (66.5 mi) to the Quebec boundary just east of Kearns. At the provincial boundary, the highway continues eastward as Route 117. From Highway 11 at Kenogami Lake eastwards to the Quebec boundary, Highway 66 is designated as part of the Trans-Canada Highway.

Matachewan is a township in Timiskaming, Northeastern Ontario, Canada, located at the end of Ontario Highway 66 along the Montreal River. The name is derived from the Cree word for "meeting of the currents".