The 1675 deed can be found LDS Film #0005593, Stonington Land Records V.1-2, 1664-1714, p.57. It was recorded in Stonington as probably that was the court where deeds in surrounding areas were recorded.
The 1679 deed for 16.5 acres in Killingworth is found in LDS Film#0004621, Town of Killingworth CT Deeds, V.1 1664-1703.
In 1679 he witnesed a deed in Edgartown, MA (which is where his wife was from) Film #0911711, Dukes Co. MA Deeds.
He purchased additional small amounts of acreage in Killingworth in 1686 and twice in 1688.
If it is inconvenient for you to access LDS films, I will be glad to send copies via email attachment if you will send your email address. My address is k7rose05@comcast.net.
Your statement that Augustine Williams owned 2,000 acres in Hebron is new to me. There is no mention of this in land transactions following his death. I would certainly like to learn about it.
I assume that you are one of us thousands who are descended from Augustine and his many children. My descent begins with his oldest child, Thomas, and continues to my paternal great-grandmother, Samantha Williams, who married my great-grandfather.
The clerks in Stonington et al are not very cooperative. They likely have become jaded over the years fending off the many inquiries they receive re Augustine.
No one so far as I know has ever traced his origins in England. If you are interestd in corresponding about any of this, I would be glad to hear.
Karen Ermutlu