I was looking through "Webster's Guide to American History",c1971, researching basic issues of the War of 1812 and was surprised to find this from 1799. "First Negro minstrel act is shown in the play "Oroonoko", produced in Boston, when an actor made up in black-face sings "The Gay Negro Boy," accompanying himself on banjo." No source was given.
I did a quick look on the internet and found some references to it, however.
There are a number of references to it in Google books, but it all seems to be from the same account. This is a great find, I had never heard this reference before.
Bob Carlin mentions it in his book "The Birth of the Banjo". chapter two I believe