Definitely not a Kentucky gun. There was a younger John Judy who was probably a gunsmith, but the only record we have of him is a short reference collected by Jim Whisker that John A. Judy was a runaway apprentice of gunsmith Samuel Thompson of Georgetown, District of Columbia [Washington D. C.] in 1817. That man would be about the right age for your rifle. But if he was working as a gunsmith about 1840, none of the major reference books mentioned it... including Ohio and Illinois books. I doubt he was related to the very early Jacob Judy of KY and IL, since I don't know how one of his kids would have gotten all the way back to the District of Columbia.
Shelby Gallien