While looking for the children of a Revolutionary War patriot who is also my ancestor, I came across this listing in the Barbour Collection (Connecticut Vital Records) :
"Thaddeus, Col. had Negro Cato b. May 4, 1785, aff. made to Oliver Stanley, J.P.. I'm assuming that aff, is affirmation and J.P. is Justice of the Peace.
Surname: Cook, Place Wallingford, New Haven, Connecticut.