Unlike the Washington Street Elevated which was built as the same time with a similar design, the Charlestown El was located very near Boston Harbor and the Mystic River tidal estuary, and was thus continually exposed to accelerated corrosion caused by salt air.
The elevated was also unpopular with many local residents, as it was noisy and blocked out sunlight to Main Street.
In the 1960s, it was determined that a replacement elevated would not be wise to build, and that a full-length replacement tunnel would be too expensive.

Instead, the Haymarket North Extension project consisted of a tunnel segment from Haymarket near Boston's downtown through a new underground stop at North Station, then under the Charles River to a portal near Community College.
From there the extension was built along the Haverhill Line commuter rail right of way, lowering land acquisition difficulties.

When planning the line in the mid-1960s, the MBTA decided that the 40-acre Wellington Dump site, located south of the previous station sites, was the best location for a rapid transit stop to serve the east part of Medford.
The new site provided ample room for parking and bus transfer areas, as well as a maintenance depot to replace the Sullivan Square shops (which were being torn down with the Elevated), plus easy access to Route 16 and Route 28.

Wellington Yard opened on July 15, 1975, followed by the station on September 6, as part of the second phase of the Haymarket North Extension.
Wellington was the first station on the line to serve an area that had not previously had rapid transit, unlike Sullivan Square and Community College which approximately replaced former elevated stations.
Wellington was the northern terminus of the Orange Line until Malden Center opened on December 27, 1975, and some trains terminated at Wellington until Oak Grove opened on March 20, 1977.

From February 1 to December 16, 1981, Malden Center and Oak Grove stations were closed on Sundays as part of systemwide austerity program.
Wellington was the northern terminus of the line on these days, with a bus shuttle run to the closed stations.

Wellington station was not originally accessible.
Addition of elevators at Wellington and Sullivan Square began in 1991.
Unlike the Washington Street Elevated which was built as the same time with a similar design, the Charlestown El was located very near Boston Harbor and the Mystic River tidal estuary, and was thus continually exposed to accelerated corrosion caused by salt air. The elevated was also unpopular with many local residents, as it was noisy and blocked out sunlight to Main Street. In the 1960s, it was determined that a replacement elevated would not be wise to build, and that a full-length replacement tunnel would be too expensive.
Instead, the Haymarket North Extension project consisted of a tunnel segment from Haymarket near Boston's downtown through a new underground stop at North Station, then under the Charles River to a portal near Community College. From there the extension was built along the Haverhill Line commuter rail right of way, lowering land acquisition difficulties.
When planning the line in the mid-1960s, the MBTA decided that the 40-acre Wellington Dump site, located south of the previous station sites, was the best location for a rapid transit stop to serve the east part of Medford. The new site provided ample room for parking and bus transfer areas, as well as a maintenance depot to replace the Sullivan Square shops (which were being torn down with the Elevated), plus easy access to Route 16 and Route 28.
Wellington Yard opened on July 15, 1975, followed by the station on September 6, as part of the second phase of the Haymarket North Extension. Wellington was the first station on the line to serve an area that had not previously had rapid transit, unlike Sullivan Square and Community College which approximately replaced former elevated stations. Wellington was the northern terminus of the Orange Line until Malden Center opened on December 27, 1975, and some trains terminated at Wellington until Oak Grove opened on March 20, 1977. 
From February 1 to December 16, 1981, Malden Center and Oak Grove stations were closed on Sundays as part of systemwide austerity program. Wellington was the northern terminus of the line on these days, with a bus shuttle run to the closed stations.
Wellington station was not originally accessible. Addition of elevators at Wellington and Sullivan Square began in 1991.
Wellington station (MBTA)