Running across this again, and having relocated since I started the thread, back to my southwestern Ontario home turf, I became curious.
As a kid, I wrote a bunch about local history here. John Graves Simcoe was one of the leading characters.
https://en.wikipedia.org/wiki/John_Graves_SimcoeJohn Graves Simcoe (25 February 1752 – 26 October 1806) was a British Army general and the first Lieutenant Governor of Upper Canada from 1791 until 1796 in southern Ontario and the watersheds of Georgian Bay and Lake Superior. He founded York (now Toronto) and was instrumental in introducing institutions such as courts of law, trial by jury, English common law, and freehold land tenure, and also in the abolition of slavery in Canada.
... Simcoe was the only surviving son of Cornishman John (1710–1759) and Katherine Simcoe (d. 1767). His parents had four children, but he was the only one to live past childhood; Percy drowned in 1764, while Paulet William and John William died as infants. ... The family then moved to his mother's parental home in Exeter. His paternal grandparents were William and Mary (née Hutchinson) Simcoe.
https://www.familysearch.org/ark:/61903/1:1:NKY7-5YSName John Graves Simcoe
Spouse's Name Elizabeth Posthuma Gillam
Event Date 30 Dec 1782
Event Place Buckerell,Devon,England
He was born in Northamptonshire. I'm wondering, given the apparent maternal familial Exeter connection, whether his "Graves" came from his mother's side, about which nothing seems to be known, and how remote his connection with Thanckes might have been.
Just idle historical curiosity.