Harwich to Brewster.
Cosigned with MA 39 in Harwich.
In 1928, 124 connected Southbridge to Auburn via Charlton City. Part of this route is now numbered MA 169.
The current 124 was originally MA 24 from 1933 until 1958. When the highway from Fall River to Boston was numbered 24, this route was renumbered to 124.