Commenter RJO is very knowledgeable about Massachusetts gravestone carvers, so I'm posting a few pics so that he (or anyone else) can determine whether this carver is indeed John Dwight of Shirley, MA (see an example of Dwight's work here).
I think that these four/five stones were carved by the same person. That opinion is based on the distinctive eye capsules, similarities in border design, and the fact they are made of slate, a material that was not often used in eastern CT. I'm not sure that the Thankfull Payson stone (#5) fits in this group, particularly since it is so much earlier than the others, but there are stylistic similarities.
Another theory is that only the Scarborough stone was carved by Dwight, while the others were carved by someone else. There is a Markers article called "The John Dwight Workshop in Shirley, MA, 1770-1816," but I haven't read it, so I don't know whether those were its active years or only the years covered in the article. I can check at the library tomorrow. Most of these stones are pre-1770, so it's unlikely that they came out of the shop in Shirley.
Joseph Scarborough, Brooklyn, CT, 1771
Abigail Perrin, Brooklyn, CT, 1767
Penelope Williams, Pomfret, CT, 1764
Mary Grosvenor, Pomfret, CT, 1770
Thankfull Payson, Pomfret, CT, 1758
I'm also open to theories as to why stones from a Shirley, MA carver are turning up in eastern CT. This sometimes happens when a carver moves away from his birthplace and continues to send stones back home (as when Zerubabel Collins moved to Vermont from CT) or when people moved away and continued to buy gravestones from their hometown carvers. Distinctive stones can also turn up in far-off places when two carvers developed similar styles under the tutelage of a single master and set up their own shops in different towns. I don't know what the case is here. In order to formulate a good guess, I'd have to know whether Dwight stones are common in other towns south of Worcester but closer to Shirley (Auburn, Oxford, Webster).