I looked at my file on the McWains and an old letter from Ruth Ostlund who is a decendent of ASA McWain son of Andrew II of Bolton. Andrew II married Polly Lambson (sp?) but she did not mention in her tree anything about Silas.
Silas is marriage was recorded in Putney in 11/17/1791 where my family (William,Andrew and John) William built a house west of town in about 1770. They were all from Bolton MA and their Mother Hezidiah was also buried on William's farm cemetery her husband Andrew I died in MA 1756. So it seems likely that Silas was from MA as was indicated in the 1850 census of Ripton. Rochester lists the children of Silas & Nabby Hubbard as Abigail Andrew,Itharner and Josiah .
I think he is likely a son of another brother James who stayed in MA.
That is all I could find quickly. But I am trying to load my years of notes into my computer and would love to share family trees with others.
Lyman McWain (firstname.lastname@example.org