The Berkshire Division (Housatonic Railroad) consisted of a main line from Bridgeport to Pittsfield with branches to New Haven, Norwalk and West Stockbridge. At some point Conrail sold off most of the lines to a new Housatonic Railroad.
http://www.catskillarchive.com/rrextra/abnere2.Html has some good information in the section on the Housatonic Railroad:
The New Haven and Derby Railroad was opened New Haven to Ansonia (or, Derby Jct.,) August 5, 1871. The Railroad YMCA on South Orange Street, New Haven, was formerly the New Haven and Derby Depot. This building was later moved 50 feet to its present location.
The New Haven and Derby engine house was located at West Street, New Haven.
November 14, 1888, the New Haven and Derby opened an extension, Derby Jct. to a point in Huntington, 3.79 miles.
November 28, 1888 the Housatonic Railroad opened a branch from Botsford to connect with New Haven and Derby extension, 9.79 miles. Old timers used to refer to this portion of the road as the extension and at that time freight trains were run from New Haven to Wilson Point via Botsford, Hawleyville and Bethel.
The New Haven and Derby Railroad was leased to the Housatonic Railroad July 9, 1889 and the Housatonic Railroad was leased to the New York, New Haven and Hartford September 10, including the Danbury and Norwalk and the New Haven and Derby Railroads. Passenger trains of the former Housatonic Railroad, known for many years as the Berkshire Division, were run to the Union Station, New Haven.