Dorchester and Milton Branch Railroad
The Dorchester and Milton Branch Railroad was incorporated April 16, 1846 as a branch off the Old Colony Railroad main line from Boston to Plymouth. William Richardson, Edmund P. Tileston, Asaph Churchill, Jonathan Ware, Mark Hollingsworth joined to form the corporation.
“Said company may locate, construct, and maintain a railroad, with one or more tracks, within the towns of Dorchester and Milton, in the county of Norfolk, commencing at the most convenient point, at or near the depot of the Old Colony Railroad, at Neponset Village, so called, in Dorchester, and thence running, on the most eligible route, through the southeasterly art of the town of Dorchester, to a point eastwardly of the road leading from Dorchester to Milton, over Milton Hill, then crossing Neponset river, and thence running through the northerly part of the town of Milton, to some convenient point in Dorchester or Milton, at or near the Upper Mills, so called.”
The line was opened for public use in December, 1847.
The following is from Wikipedia, a website accessed March 23, 2018.
The 3.3 mile road was completed on December 1, 1847 from Neponset Village in Dorchester, Massachusetts through the town of Milton to the village of Mattapan.
The line was leased to the Old Colony Railroad from January 1, 1848 to January 1, 1856, and operated under contract by the Old Colony from 1856 to 1863 when it was merged into the Old Colony and Fall River Railroad Company. In 1893, it became part of the New York, New Haven and Hartford Railroad as part of the lease of the entire Old Colony Railroad network.
From 1848 to 1872, commuter rail service to Ashmont operated over the whole line (as the Milton Branch or Neponset Branch). When the Shawmut Branch opened in 1872, Mattapan commuter service was diverted over the new line, and the Milton Branch east of Shawmut Junction saw little passenger traffic. After the Shawmut Branch was closed on September 6, 1926 for construction of the Dorchester Extension, all Mattapan passenger and freight service was rerouted via Neponset over the Milton Branch. Local residents lobbied for the restoration of a flag stop at the Granite Avenue (Granite Bridge) station to serve the Cedar Grove and Ashmont neighborhoods, a request granted in October 1926.
The first section of the Ashmont-Mattapan High Speed Line opened from Ashmont to Milton on August 26, 1929.
The high-speed trolley line entered the center of the Milton Branch right of way on a flyover, and ran to Milton flanked by the Milton Branch tracks. Commuter rail service ended when the trolley line reached Milton, over the protests of Milton residents who wanted limited service kept while the trolley line was extended to Mattapan. After four more months of construction, the full trolley line was opened to Mattapan on December 21, 1929.
Freight service was retained on the line as far as Milton until the 1980s. The Neponset Trail, a multi-use rail trail, was later built on the right-of-way from Neponset Avenue to Central Avenue. From Shawmut Junction to Central Avenue, it shares the corridor with the MBTA trolley line, and occupies only the former northern freight track. An extension of the trail to Mattapan, largely parallel to the line rather than adjacent to it, will open in 2017.
 Private and Special Statutes of the Commonwealth of Massachusetts, from January 1838 to May 1848 …Volume 8. (Boston, 1848), 645.
 Massachusetts. Board of Railroad Commissioners. Sixth Annual Report of the Board of Railroad Commissioners. (Boston, 1874), 138.