By the time of the Washington administration, certainly the richest man in the U.S. was William Duer, the speculator. He was also the under-secretary of the Treasury, and got caught up before very long in all sorts of scandals. I believe he was the one who embezzled the funds for Hamilton's famous industrial project in Paterson, New Jersey.
I don't know if Duer was the richest at the time of the Revolution. I doubt it.
Tom Frank