The Hartford and New Haven Railroad of Connecticut was chartered in 1833 to build a railroad between Hartford and New Haven. The grandfather of J. P. Morgan was an original investor, laying the foundation for the long association between Morgan and the railroads of New England. It commenced full operation in 1839, with half of the line opening the prior year. The Hartford and Springfield Railroad was incorporated April 5, 1839, and built the Massachusetts portion of the Hartford-Springfield route, which opened in 1844. The New York and New Haven Railroad was incorporated in 1844.
In 1845, the Hartford and New Haven merged with the Hartford and Springfield Railroad to form the New Haven, Hartford and Springfield Railroad. This new railroad changed its name to the Hartford and New Haven Railroad in 1847.
The Hartford and New Haven and the New York and New Haven were consolidated into the New York, New Haven and Hartford Railroad in 1872.