The Ontario Northland Railway (reporting mark ONT) is a Canadian railway operated by the Ontario Northland Transportation Commission, a provincial Crown agency of the government of Ontario.
Originally built to develop the Lake Timiskaming and Lake Nipissing areas, the railway soon became a major factor in the economic growth of the province. After decades of difficult construction through the Canadian Shield, workers reached James Bay in 1932. While blasting the route through the shield, geologists discovered deposits of valuable minerals such as gold, silver, copper and nickel. The railway also made it possible to exploit the timber resources of Northern Ontario.
Its north–south mainline is located entirely in Ontario, starting at its southern terminus at North Bay, running northward through Cobalt, New Liskeard, Cochrane, and on to its northern terminus at Moosonee, several miles south of the shore of James Bay. There is one major branchline running eastward from Swastika through Kirkland Lake and over the Quebec border to end at Rouyn-Noranda. The railway's branch from Swastika to Rouyn-Noranda, including 40 kilometres of track in Quebec, is operated by a subsidiary, the Nipissing Central Railway.Shorter spur lines also exist running west from Rock Junction to Sherman Mine, south-west from Porquis Junction to Kidd Creek Mine, about 22 km east of Timmins, north-east from Porquis to Iroquois Falls and south from Opaz Junction to Agrium mine site. Several other mining spurs opened and closed with the mines they served. Since 1993, the ON operates a section of the National Transcontinental Railway running west from Cochrane to Calstock.