King’s Highway 89, commonly referred to as Highway 89, is an east–west provincially maintained highway in the southwestern portion of the Canadian province of Ontario. The route stretches 107 kilometres (66 mi) from Highway 400 just east of Cookstown in the east to the junction Highway 9 and Highway 23 in Harriston. The principal urban centres along the highway include Alliston, Shelburne and Mount Forest.
Highway 89 was established in 1937 as a result of the rerouting of Highway 9 between Orangeville and Highway 27. In 1963, the route was extended west to Palmerston and east to Highway 400. Plans were conceived during the late 1970s to push the highway further east to Highway 12 via Ravenshoe Road, resulting in a brief extension to Highway 11. However, environmental protest over the chosen route through the Holland Marsh resulted in the cancellation of plans in 1986. In 1997, the section between Highway 400 and Highway 11 was decommissioned. The most recent change to the route took place in 2003, when the section of Highway 89 between Palmerston and Harriston was renumbered as part of Highway 23, creating a shared terminus at a junction with Highway 9.