The Montreal Subdivision is a railroad line owned by the St. Lawrence and Adirondack Railway[1] and Canadian National.

At its south end, the St. Lawrence Subdivision continues south; its north end was at Adirondack Junction, a junction with the Canadian Pacific Railway's Adirondack Subdivision, along which it had trackage rights north over the Saint-Laurent Railway Bridge into Montreal.

[3][4] The piece from Huntingdon, Quebec, north to Salaberry-de-Valleyfield opened in 1892 as part of the St. Lawrence and Adirondack Railway.

The line from Valleyfield to Beauharnois was originally a branch of the Grand Trunk Railway, built in the 1880s.

[citation needed] The StL&A leased this line, and in 1897, they opened an extension from Beauharnois to Adirondack Junction.