The Agricultural Branch Railroad was a railroad in Massachusetts. It was incorporated by the Legislature of Massachusetts on April 26, 1847, to provide a rail connection between Framingham and Northborough through the town of Southborough and a small portion of the city of Marlborough. Service began on December 1, 1855.
A 1.5-mile branch off the 13.2-mile main line from Marlborough Junction into Marlborough was added in June 1855. In July 1866, the railroad opened a 14-mile extension from Northborough to the Fitchburg and Worcester Railroad at Pratts Junction in Sterling via the towns of Berlin, Boylston, Lancaster, and Clinton, bringing the entire line up to 28.7 miles of track and establishing connections to Fitchburg and the growing railroad hub of Worcester. On May 20, 1867, the name of the railroad was changed to the Boston, Clinton and Fitchburg Railroad, and in 1869, it merged with the Fitchburg and Worcester Railroad.
On April 1, 1872, the Boston, Clinton, and Fitchburg Railroad signed a twenty-year lease of the nearby Framingham and Lowell Railroad, which connected with the Boston, Clinton, and Fitchburg Railroad in Framingham and provided a connection to the major mill city of Lowell.
On January 1, 1873, the Boston, Clinton, and Fitchburg Railroad signed a fifty-year lease of the Mansfield and Framingham Railroad, providing a connection to the Boston and Providence Railroad and the Taunton Branch Railroad in Mansfield. On July 1, 1873, the Taunton Branch Railroad merged with the New Bedford and Taunton Railroad and the Middleborough and Taunton Railroad to form the New Bedford Railroad. Less than a year later, on February 2, 1874, the Boston, Clinton, and Fitchburg Railroad entered into a fifty-year lease agreement with the New Bedford Railroad, which provided access to the deep water whaling port at New Bedford. On June 1, 1875, the Boston, Clinton, and Fitchburg Railroad consolidated with the Mansfield and Framingham Railroad, and exactly one year later, on June 1, 1876, the Boston, Clinton, and Fitchburg Railroad merged with the New Bedford Railroad to form the Boston, Clinton, Fitchburg and New Bedford Railroad. In 1879, the Boston, Clinton, Fitchburg and New Bedford Railroad was leased to the Old Colony Railroad for 999 years, but on October 1 of that same year nonetheless extended its lease of the Framingham and Lowell Railroad to 998 years. On September 10, 1881, the Framingham and Lowell Railroad was deeded on execution sale to the Boston, Clinton, Fitchburg, and New Bedford Railroad, forming the railroad's largest network with 126.2 miles of track system-wide.