The Plymouth Subdivision is a freight railroad line in the U.S. state of Michigan. It is owned by CSX. It connects the Plymouth Diamond at milepost CH 24.5 to Grand Rapids at CH 148.1, passing through the Lansing metropolitan area en route. Other towns served include Brighton, Howell, Williamston, Grand Ledge, and Lake Odessa. Operationally, it is part of the CSX Chicago Division, dispatched from Calumet City, Illinois.