The old New Haven to Northhampton line was started in 1846, when the New Haven & Northampton Canal Co. was authorized to build a railroad to replace the canal.
In 1848, the NH&N was leased to the NY&NH (before the NY&NH bought the NH&H to create the NY,NH & H0) who operated it until 1869, then the NH&N ran it until 1887, when the NH bought it, they ran passenger trains until 1929, but until 1969, when the PC got it it was mostly intact (The New Hartford to Collinsville branch was abandoned in 1958, the Shelburne Junction to South Deerfield was gone by 1923, and the rest of the line -South Deerfield toNorthampton – in 1943 and the Willamsburg to Florence in 1962 was abandoned, but the main line was in use). In 1969 PC abandoned the Collinsville to Farmington branch, along with the Florence – Easthampton branch and the main line from Easthampton to Northampton. In 1976, the USRA took out the middle section from Simsbury to Westfield saying it wasn’t needed, the state of Connecticut subsidized the operations from Avon to Simsbury (there was a few customers in Simsbury). In 1981, Connecticut stopped subsidizing freight operations from Avon north to Simsbury, then the B&M (who in my opinion should not RUN a model train layout, let alone a real railroad, acquired the New Haven to Avon line – with the Westfield to Easthampton line taken over by Pioneer Valley. In 1987 New Haven to Cheshire was abandoned (low clearences , so modern boxcars couldn’t go under them), then in 1991 B&M got rid of the Plainville to Avon track. In 1996, B&M got rid of Cheshire to Southington line – and the rest of the line is mostly out of service. Most of the line is now trails. Plainville is the hub of the PAR (nee B&M) operations in Connecticut.
Canal Line Southern end in the 1980’s. Between Cheshire and Hamden.
See lots more on abandoned railroads in Connecticut