Kennedy also polled worse in some counties than Humphrey would do 8 years later. Humphrey took Plymouth and Kennedy didn't (Johnson took every county, but that of course was an exceptional election)
I assume these counties were disproportionately Protestant areas (by Massachusetts standards)? The 1960 results had a heavy Catholic for Kennedy/Protestant for Nixon split, moreso than pretty much any election ever (1928 as well, possibly even greater than 1960).
Plymouth and Barnstaple were Protestant, rich, and very traditionally Republican back then.
they still are, lewis. of course their republicanism is relative. those two counties are the two most republican in the state. True of course. Well, most of the time anyways (as far as presidentials are concerned. They may be more dependable in state politics, I don't know about that.)
The northern end of it is run-of-the-mill suburban.
Both counties also have a very long-established rural/exurban/touristic/wealthy peoples' second homes mix. (Kennedy voted in Barnstable County.)