Here is thumbnail of what I have gathered in:
Early years: He was born in Northborough, Middlesex, MA on 10 Jun 1738 to William Williams (12 Oct 1710) and Tabitha Pearsons (11March 1713). As a young man he became involved with the Rangers, serving in the French and Indian War. Reading a history of the Rangers in that area, they spent much time in the Coos County area of present day New Hampshire and west across the Connecticut River in present day Vermont. This area was contested between America and Canada for years. He left that duty as a Captain and one who had gained a distinguished record as a later letter to the Continental Congress by Ethan Allen attest.
On 5 Jan 1762, he marries a Lancaster, MA girl named Zilpah Wilder, born in Reading, MA to Asaph Wilder and Zipporah Wheeler.
William was an enterpriser and raised a saw mill in Reading, MA, presuming he operated it for a while. His family grew as first Lydia was born in 1764, Zipporah in 1765 and Phoebe in 1768, all in Reading. In 1764 he received a grant for land in Bennington from George III but there is no evidence he lived there. There are records he received grants in several spots in Vermont through the years.
Soon after they started moving. Something they did a lot of for the rest of their lives. First to Marboro,VT, where he raised the first framed building in the town, it was a barn. Then to Wilmington, VT where they kept residence. In the Spring of 1775 he is a delegate to the First Provincial Congress of New York (that state was in dispute over ownership of the so called New Hampshire Grants, soon to be Vermont). In 1776 he is re-elected to that position and while participating in that role, he is offered a Colonelcy in the state militia. He takes it. Returns to Wilmington and what was then called Cumberland County to raise a regiment. (There is 500 + page document you can view on line call the "The Records of the Governor and Council of Vermont, 1775-1777 --and later" In one of the minutes of the Council of Safety, Williams informs them of his difficulty in raising men, they keep going home. As the Battle of Bennington nears in April 1777, he tells General Stark he needs help in keeping the forces together. There is much more in those pages on Williams)
He succeeds in marshaling his Regiment and moved to Bennington to join forces with Gerneral Stark and they fight the decisive battle together with distinction and success. A monument in Wilmington with his name and all those who served from the town.
During and after the war he represents what was then Cumberland and later Windham County in the colonial/state governments.
Near the end of the war, his family grows. Asaph is born in 1779 and William in 1782. Most probably in Wilmington. (which confusingly was once called Draper but no one there liked the name so it became Wilmington again).
Dates and places of their later moves are elusive at the moment.
Both his grave and that of Zilpah are located in the Piper Hill Cemetery just south of Stewartstown, NH. They died within days of each other in December 1822. An authority and author on the regions cemeteries, says his gravestone begins with "In Memory Of....." Nancy Dugan the author tells me that usually indicates he died elsewhere but was buried there. He had an SAR plaque by his grave.
If you have not read "History of Eastern Vermont" by Benjamin H. Hall, 1853 you will find it on line or Abe books. A three page bio of William begins on p. 178. It starts with a copy of his signature.