wood turtles have no hinges and so cannot close their shells. i wonder if its ahuger gulf coast and (perhaps you over estimated its size) or if its an escaped pet malayan box turtle. This would also not be out of the question for awood turtle as they are popular pets and they turn up in strange places now and then
Sure its not a gopher tortoise?
As for the long island easterns the largest i ever saw in twenty years there was about 10 inches: :