The Grand Trunk Western Railroad Company was an American subsidiary of the Grand Trunk Railway, later of the Canadian National Railway 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.

The Grand Trunk Railway was a railway system that operated in the Canadian provinces of Quebec and Ontario and in the American states of Connecticut, Maine, Michigan, Massachusetts, New Hampshire, and Vermont. The railway was operated from headquarters in Montreal, Quebec, with corporate headquarters in London, United Kingdom. It cost an estimated $160 million to build. The Grand Trunk, its subsidiaries, and the Canadian Government Railways were precursors of today's Canadian National Railway.