City (pop., 2001: 109,016), west-central Ontario, Canada. It is located on the northwestern shore of Lake Superior. Its first settlement was a French fur-trading post c. 1678. In the 1870s and '80s silver strikes and the arrival of the Canadian Pacific Railway brought prosperity to the twin towns of Port Arthur and Fort William that had grown up there. Their rivalry was resolved with the unification of their harbour facilities in 1906; the towns merged in 1970 and created the city of Thunder Bay. It is one of Canada's busiest ports, with grain storage and transshipment depots; other industries include shipbuilding.