I know that my ancestor, Garrett Terhune (son of William S.), was born in 1757 in Somerset City, NJ. He had a daughter, Sarah, born in 1791. So, perhaps your relative was a brother/cousin of hers (the dates would be right - and it's a place to start)?? My sister says there is a website of "New Jersey Terhunes" but I've not had time to investigate. If you find that, maybe you could get some answers. Good luck!