Massachusetts's 12th congressional district is an obsolete district that was first active 1795–1803 in the District of Maine and 1803–1843 in Eastern Massachusetts. It was later active 1883–1893 in Western Massachusetts and 1893–1983 in Eastern Massachusetts. It was most recently eliminated as a result of the redistricting cycle after the 1980 census. Its last congressman was Gerry Studds, who was redistricted into the Massachusetts's 10th congressional district. Notable persons elected to the U.S. House of Representatives from the 12th congressional district include John Quincy Adams, following his term as president, and James Michael Curley, four-time Mayor of Boston.

Cities and towns in the district

1790s–1830s

1880s–1900s

1910s

Suffolk County: Boston Wards 13, 14, 15, 16, 17, 20, 24.

1920s

Boston (Wards 9, 10, 11, 12, 17, 18, 19, 20, 21).

1940s

Boston (Wards 6, 7, 8, 9, 11, 13, 14, 15, 16, 17).

1950s–1980s

List of members representing the district