[3] Conrail's New England assets were absorbed by CSX Transportation in 1999, which became CSO's new connection in West Springfield and New Haven.

[10] The State of Connecticut began Hartford Line commuter rail service in June 2018.

Major commodities transported include lumber, steel, and carbon dioxide, which are mostly imported from elsewhere.

[14] As Amtrak is strictly a passenger railroad, Connecticut Southern provides freight service over the entirety of the line, on which it has trackage rights.

[2][15] On this line, Connecticut Southern interchanges with CSX at Cedar Hill Yard in North Haven and at another yard in West Springfield, with Pan Am Southern in Berlin, and with both fellow Genesee and Wyoming subsidiary Providence and Worcester Railroad and the Central New England Railroad in Hartford.

[19] Rail service to Suffield had ended by July 2009, and Connecticut Southern filed for abandonment of the 2.4 miles (3.9 km) of track leading to the town in 2012.

CSO announced they would remove the railroad ties and steel tracks for salvage in their abandonment filing.

The town of Suffield attempted to stop the abandonment and salvage of the tracks to preserve them for potential future use.

[18] Bradley Airport is a CSO customer, as is Camp Hartell, an Army National Guard facility in Windsor Locks.

[16] Connecticut Southern operates this line between Hartford and the end of track in Manchester, beyond which the right of way has been converted into the Hop River State Park Trail.

[16] CSO filed for abandonment of the final mile of this line in November 2021; the right-of-way was then purchased by the Connecticut Department of Transportation to allow removal of a grade crossing as part of an intersection improvement project.