I'm descended from the marriage of Edward Tonkin (chr. 14 Dec 1777 at Kea, Cornwall) and Ann Trevethan (chr. 24 May 1779, at Kenwyn, Cornwall). They were married at Kenwyn, Cornwall, on 24 Oct 1801.
As yet solidified information I have right now is that Ann was the daughter of Samson Trevethan and Jenifer Richards, who married in 12 Feb 1763 at Kenwyn. It appears they had a son Henery, who was born only a year after their marriage. But their other two children -- Ann and Sampson -- were born much later.
Again, I have yet to confirm the data on the parents of Ann's parents and siblings. However, my family's link to her and her husband Edward Tonkin is rather solid. If you think there might be a connection, drop me an e-mail.