The Grand Trunk Western Railroad Company (reporting mark GTW) is an American subsidiary of the Canadian National Railway (reporting mark CN) operating in Michigan, Illinois, Indiana, and Ohio. Since a corporate restructuring in 1971, the railroad has been under CN's subsidiary holding company, the Grand Trunk Corporation. Grand Trunk Western's routes are part of CN's Michigan Division. Its primary mainline between Chicago and Port Huron, Michigan serves as a connection between railroad interchanges in Chicago and rail lines in eastern Canada and the Northeastern United States. The railroad's extensive trackage in Detroit and across southern Michigan has made it an essential link for the automotive industry as a hauler of parts and automobiles from manufacturing plants.