| Name | Mark | System[nb 1] | From[nb 2] | To[nb 3] | Successor | Description | References |
| Boston, Hartford and Erie Railroad | | NH | 1863 | 1874 | New York and New England Railroad | | |
| Boston and Maine Corporation | BM | | 1983 | | | Still exists as a lessor of Pan Am Railways operating subsidiary Springfield Terminal Railway | |
| Boston and New York Air-Line Railroad | | NH | 1875 | 1907 | New York, New Haven and Hartford Railroad | | |
| Boston and New York Central Railroad | | NH | 1853 | 1858 | Midland Railroad | | |
| Boston, Norwich and New London Railroad | | NH | 1832 | 1836 | Norwich and Worcester Railroad | | |
| Branch Company | | NH | 1845 | 1850 | Hartford and New Haven Railroad | Built a short spur between the H&NH main line in Hartford, and the Connecticut River. | [7] |
| Central New England Railway | CNE | NH | 1899 | 1927 | New York, New Haven and Hartford Railroad | | |
| Central New England and Western Railroad | NH | | 1889 | 1892 | Philadelphia, Reading and New England Railroad | | |
| Central Vermont Railroad | | CN | 1873 | 1899 | Central Vermont Railway | | |
| Central Vermont Railway | CV | CN | 1899 | 1995 | New England Central Railroad | | |
| Colchester Railroad | | NH | 1876 | 1907 | New York, New Haven and Hartford Railroad | | |
| Connecticut Central Railroad[nb 4] | CCCL | | 1987 | 1998 | Providence and Worcester Railroad | Shortline railroad that operated former Conrail trackage in and around Middletown, Connecticut. | [8][9] |
| Connecticut Central Railroad | | NH | 1871 | 1887 | New York and New England Railroad | | |
| Connecticut Valley Railroad | | NH | 1868 | 1880 | Hartford and Connecticut Valley Railroad | | |
| Connecticut Western Railroad | | NH | 1868 | 1881 | Hartford and Connecticut Western Railroad | | |
| Consolidated Rail Corporation | CR | | 1976 | 1999 | CSX Transportation | | |
| Danbury and Norwalk Railroad | | NH | 1850 | 1907 | New York, New Haven and Hartford Railroad | | |
| Danbury Terminal Railroad | DTRR | | 1993 | 1996 | Housatonic Railroad | | |
| East Granby and Suffield Railroad | | NH | 1901 | 1908 | Central New England Railway | | |
| East Thompson Railroad | | NH | 1853 | 1858 | Boston and New York Central Railroad | | |
| Fairfield County Railroad | | NH | 1835 | 1850 | Danbury and Norwalk Railroad | | |
| Farmington Valley Railroad | | NH | 1852 | 1862 | New Haven and Northampton Railroad | Built an extension of the New Haven and Northampton Railroad from Granby to the Massachusetts state line, leased by the NH&N soon after completion. | |
| Hartford and Connecticut Valley Railroad | | NH | 1879 | 1892 | New York, New Haven and Hartford Railroad | | |
| Hartford and Connecticut Western Railroad | | NH | 1881 | 1947 | New York, New Haven and Hartford Railroad | | |
| Hartford and New Haven Railroad | | NH | 1833 | 1872 | New York, New Haven and Hartford Railroad | The first railroad built in Connecticut; construction began in 1836. Opened from New Haven to Hartford in 1839, to Springfield, Massachusetts in 1844. Merged with the New York and New Haven Railroad in 1872. | |
| Hartford and Providence Railroad | | NH | 1847 | 1849 | Hartford, Providence and Fishkill Railroad | | |
| Hartford, Providence and Fishkill Railroad | | NH | 1849 | 1879 | New York and New England Railroad | | |
| Hartford and Springfield Railroad | | NH | 1835 | 1847 | Hartford and New Haven Railroad | Formed in 1835 to build north from Hartford to the Massachusetts state line. Owned and operated by the Hartford and New Haven Railroad, merged into that company in 1847. | [12] |
| Housatonic Railroad | | NH | 1836 | 1898 | New York, New Haven and Hartford Railroad | | |
| Manchester Railroad | | NH | 1833 | 1847 | Hartford and Providence Railroad | | |
| Manufacturers' Railroad[nb 5] | | NH | 1893 | 1907 | New York, New Haven and Hartford Railroad | | |
| Meriden and Cromwell Railroad | | NH | 1882 | 1888 | Meriden, Waterbury and Connecticut River Railroad | | |
| Meriden and Waterbury Railroad | | NH | 1887 | 1888 | Meriden, Waterbury and Connecticut River Railroad | | |
| Meriden, Waterbury and Connecticut River Railroad | | NH | 1888 | 1896 | Middletown, Meriden and Waterbury Railroad | | |
| Middletown Railroad | | NH | 1844 | 1850 | Hartford and New Haven Railroad | Formed by citizens of Middletown to connect their city to the H&NH main line in Berlin. Built in 1848, purchased by the H&NH in 1850. | [7] |
| Middletown Extension Railroad | | NH | 1857 | 1861 | Hartford and New Haven Railroad | Formed to build an extension of the Middletown Railroad to the Connecticut River. Built in 1860, consolidated into the Hartford and New Haven Railroad the following year. | [13][14] |
| Middletown, Meriden and Waterbury Railroad | | NH | 1897 | 1907 | New York, New Haven and Hartford Railroad | | |
| Midland Railroad | | NH | 1858 | 1862 | Midland Land Damage Company | | |
| Midland Land Damage Company | | NH | 1861 | 1863 | Southern Midland Railroad | | |
| Naugatuck Railroad | | NH | 1845 | 1906 | New York, New Haven and Hartford Railroad | | |
| New Britain and Middletown Railroad | | NH | 1852 | 1868 | Hartford and New Haven Railroad | Formed by citizens in New Britain to construct a short branch to the H&NH in Berlin. Constructed in 1862, it was operated by the H&NH until that company absorbed it in 1868. | [7] |
| New Canaan Railroad | | NH | 1866 | 1883 | Stamford and New Canaan Railroad | | |
| New England Railroad | | NH | 1895 | 1908 | New York, New Haven and Hartford Railroad | | |
| New Haven and Derby Railroad | | NH | 1864 | 1907 | New York, New Haven and Hartford Railroad | | |
| New Haven, Middletown and Willimantic Railroad | | NH | 1867 | 1875 | Boston and New York Air-Line Railroad | | |
| New Haven and New London Railroad | | NH | 1848 | 1865 | Shore Line Railway | | |
| New Haven, New London and Stonington Railroad | | NH | 1858 | 1864 | New York, Providence and Boston Railroad | | |
| New Haven and Northampton Railroad | | NH | 1846 | 1910 | New York, New Haven and Hartford Railroad | | |
| New London Northern Railroad | | CN | 1859 | 1951 | Central Vermont Railway | | |
| New London and Stonington Railroad | | NH | 1852 | 1864 | New York, Providence and Boston Railroad | | |
| New London, Willimantic and Palmer Railroad | | CN | 1849 | 1861 | New London Northern Railroad | | |
| New London, Willimantic and Springfield Railroad | | CN | 1847 | 1849 | New London, Willimantic and Palmer Railroad | | |
| New York and Boston Railroad | | NH | 1846 | 1865 | Boston, Hartford and Erie Railroad | | |
| New York and Hartford Railroad | | NH | 1845 | 1849 | Hartford, Providence and Fishkill Railroad | | |
| New York, Housatonic and Northern Railroad | | NH | 1864 | 1882 | Housatonic Railroad | | |
| New York and New England Railroad | | NH | 1873 | 1895 | New England Railroad | | |
| New York and New Haven Railroad | | NH | 1844 | 1872 | New York, New Haven and Hartford Railroad | | |
| New York, New Haven and Hartford Railroad | NH | NH | 1872 | 1969 | Penn Central Transportation Company | | |
| New York, Providence and Boston Railroad | | NH | 1833 | 1893 | New York, New Haven and Hartford Railroad | | |
| New York and Stonington Railroad | | NH | 1832 | 1833 | New York, Providence and Boston Railroad | | |
| Norwich and Worcester Railroad | | NH | 1836 | 1976 | Consolidated Rail Corporation | | |
| Penn Central Transportation Company | PC | | 1969 | 1976 | Consolidated Rail Corporation | | |
| Philadelphia, Reading and New England Railroad | | NH | 1892 | 1899 | Central New England Railway | | |
| Rockville Railroad | | NH | 1863 | 1907 | New York, New Haven and Hartford Railroad | | |
| Rockville Branch Railroad | | NH | 1857 | 1863 | New York, New Haven and Hartford Railroad | | |
| Shepaug, Litchfield and Northern Railroad[nb 6] | | NH | 1866 | 1898 | New York, New Haven and Hartford Railroad | | |
| Shore Line Railway | | NH | 1864 | 1897 | New York, New Haven and Hartford Railroad | | |
| South Manchester Railroad | | NH | 1866 | 1976 | Consolidated Rail Corporation | | |
| Southbridge and Blackstone Railroad | | NH | 1849 | 1853 | Boston and New York Central Railroad | | |
| Southern Midland Railroad | | NH | 1863 | 1863 | Boston, Hartford and Erie Railroad | | |
| Stamford and New Canaan Railroad | | NH | 1882 | 1890 | New York, New Haven and Hartford Railroad | | |
| Thompson and Willimantic Railroad | | NH | 1857 | 1863 | Boston, Hartford and Erie Railroad | | |
| Vermont Central Railroad | | CN | 1871 | 1873 | Central Vermont Railroad | | |
| Watertown and Waterbury Railroad | | NH | 1869 | 1893 | Naugatuck Railroad | Chartered in 1869 to connect Watertown to the Naugatuck Railroad in Waterbury. Was leased by the Naugatuck Railroad upon opening in the fall of 1870, which absorbed it in 1893. | [16] |
| Windsor Locks and Suffield Railroad | | NH | 1868 | 1871 | Hartford and New Haven Railroad | Formed in 1868 to construct a branch between Suffield and Windsor Locks, where it met the H&NH. Built in 1870, it was absorbed by the H&NH in 1871. | [7] |