It runs from Boston's South Station in a southwesterly direction toward Franklin, Massachusetts.

[5] However, in the 1940s and early 1950s service, including the New Haven's Nutmeg and several unnamed trains from Boston to Hartford and Waterbury continued.

[6] It was shortened to Blackstone when the two southern spans of the bridge crossing the Quinebaug River in Putnam, Connecticut washed out during Hurricane Diane in 1955.

Service was extended to Forge Park/495 station on June 2, 1988, although the line retained its original name.

[7] In February 2020, the MBTA voted to purchase the line from Franklin to Milford for $13 million.

Phase 2 will add 3.5 miles (5.6 km) of double track between Franklin and Norfolk; it will allow headways to drop from 45 to 35 minutes.

[18][19] Intermediate stops for the 1980s iteration were at Readville and Norwood Central (plus Back Bay in 1988).

[24][25] In September 2010, the MBTA completed a study to determine the feasibility of extending regular commuter rail service to Foxboro station via the Franklin Line.

[33] In November 2020, as part of service cuts during the pandemic, the MBTA proposed to close Plimptonville along with five other low-ridership stations on other lines.

[34] On December 14, the MBTA Board voted to enact a more limited set of cuts, including indefinitely closing Plimptonville and four of the other five stations.

[38][39] As part of that schedule change, all Franklin Line trains operating via the Southwest Corridor began stopping at Ruggles station after an additional platform there was completed.

[49][50] In July 2011, the Boston Region Metropolitan Planning Organization began studying the viability of extending Franklin Line commuter rail service to Hopedale and Milford.

The study would update a 1997 MBTA evaluation that concluded costs outweighed the benefits of a possible expansion.

[7] A 2004 analysis determined that the extension would cost $70.5 million and attract about 1,800 additional riders per weekday.