Any direct links to the modern region of Cornwell?
Cornwall? I doubt it. There were former Roman towns that persisted after the Empire pulled out, and had at least some period of time as autonomous realms. Other towns just seem to have dropped dead. Paul Whitewick’s channel has stuff related to that kind of thing, plus one that appears to pertain to post-Roman Cornwall.
https://www.youtube.com/watch?v=V_PxsaZGI28
https://www.youtube.com/watch?v=qtZfzgwqUzM
https://www.youtube.com/watch?v=PUniun8bUN0