The 50-pound terra cotta head was found near where a new wing is being built.
The couple, Patrick and Janis Tooman of Sag Harbor, says they were planning construction at their home.
So their son, a contractor, put it in his truck.
He then drove to his next gig at the East Hampton Library where it was accidently unloaded.
The head was given to the Toomans as a gift from a sculptor.
The bust usually sits in their backyard.
The library has now repositioned its security cameras to prevent anyone from stealing.