The Fairmount Line or Dorchester Branch is a line of the MBTA Commuter Rail system in Boston, Massachusetts, USA. Except for a short portion in Milton, it lies entirely within Boston, running southwest from South Station through the neighborhoods of Dorchester, Mattapan and Hyde Park. Weekend service began on November 29, 2014. Most trains reverse direction at the south end at Readville, but a few continue onto the Franklin Line.
From the 1980s until 2012, the Fairmount Line had only five stations: three plus the two termini (South Station and Readville); however, three more stations were added to the line between 2012 and 2013. The first of these, Talbot Ave, opened on November 12, 2012, followed by Newmarket and Four Corners/Geneva on July 1, 2013. Due to neighborhood opposition over its design and location, another planned station, Blue Hill Avenue, has been delayed until 2019. All stations on the line are fully handicapped accessible.
The corridor currently serves mostly low-income and working-class communities. Despite frequent cancellations, a June 2016 count showed that ridership had nearly tripled from 2012.