King's Highway 27, commonly referred to as Highway 27, is a provincially maintained highway in the Canadian province of Ontario. The Ministry of Transportation of Ontario was once responsible for the length of the route, when it ran from Long Branch to Highway 93 in Waverley. Highway 27 followed a mostly straight route throughout its length, as it passed through the suburbs of Toronto, then north of Kleinburg the vast majority of the highway was surrounded by rural farmland. Today, only the southernmost 1.6 km (1 mi) from Highway 427 north to Mimico Creek is under provincial jurisdiction, the remainder of the route is maintained by the city of Toronto, York Region and Simcoe County.

The Provincial Highway Network consists of all the roads in Ontario maintained by the Ministry of Transportation of Ontario (MTO), including those designated as part of the King's Highway, secondary highways, and tertiary roads. Components of the system—comprising 16,900 kilometres (10,500 mi) of roads and 2,880 bridges —range in scale from Highway 401, the busiest highway in North America, to unpaved forestry and mining access roads. The longest highway is nearly 2,000 kilometres (1,200 mi) long, while the shortest is less than a kilometre. Some roads are unsigned highways, lacking signage to indicate their maintenance by the MTO; these may be remnants of highways that are still under provincial control whose designations were decommissioned, roadway segments left over from realignment projects, or proposed highway corridors.