The Connecticut Southern Railroad (reporting mark CSO) operates about 78 miles (126 km) of track in Connecticut and Massachusetts. It is a subsidiary of Genesee & Wyoming. The line is headquartered in East Hartford, CT and interchanges with CSX at West Springfield, Massachusetts and New Haven, Connecticut.
The railroad began operations in 1996 and was acquired by RailAmerica in 2000. Genesee & Wyoming acquired the railroad as part of its acquisition of RailAmerica in 2012.
Traffic comes mainly from construction materials, as well as food products. The CSO hauled around 23,000 carloads in 2008.