Ontario Highway 138 History - The King's Highways of Ontario

King's Highway 138 is a major collector highway serving the Counties of Stormont, Dundas and Glengarry. The highway's primary function is to connect the City of Cornwall with Highway 417. The highway was created in 1967, when a new provincial highway was designated between the Cornwall City Limits and Highway 43 at Monkland. The new highway was assumed as a King's Highway on April 3, 1967. When construction got underway on Highway 417 in the 1970s, Highway 138 was extended north from Monkland to meet the new Highway 417 east of Casselman. The extension of Highway 138 from Highway 43 to Highway 417 was designated in 1971.

A municipal connecting link extended south from Cornwall Centre Road in order to connect the otherwise discontinuous Highway 138 to Highway 401 and Highway 2. The portion of Highway 138 within the City of Cornwall was not maintained by the Ministry of Transportation. The route of Highway 138 has remained unchanged since the 1970s, although the municipal connecting link that followed Brookdale Avenue from Cornwall Centre Road to Highway 2 (Vincent Massey Drive) is now only signed as far south as Highway 401.

Highway 138 is a two-lane highway for its entire length, except for an undivided four-lane section within Cornwall. The highway passes through predominantly rural areas along its 39 km route. Services are rather scarce along this highway outside of larger communities. The speed limit on Highway 138 is 80 km/h (50 mph), unless posted otherwise. Please visit the Highway 138 Mileage Chart page for a list of mileage reference points along Highway 138.