Unthank is an interesting name: there are a few hamlets/small villages named Unthank in the North of England; there's even an Unthank Hall. However, I suspect that more people live in Norwich's Unthank Road than in all of the other places put together.
According to Ancestry, the meaning derives from Old English unthanc ‘without consent’, i.e. a squatter’s holding.
There was a boy in my high school graduating class (in New Jersey) whose name was Unthank. I thought it was an unusual name at the time but I never looked into its origins. it's interesting to know that it's prevalent in the North of England. I have never come across the name other than that one boy, and, of course, in Pepys' diary.
Chart showing the number of references in each month of the diary’s entries.