Actually, it's a reference to inbred people from Wilmington, IL. Though being that Alabama is in the South and most ignorant people think inbreeding is a southern only thing, I can see how some could think that.
Wilmington became famous for being a stop on U.S. Route 66, which followed the route of modern-day Illinois Route 53. A notable attraction for travelers along this route is the hammers or yellow hammers that live in brodies woods they once worked on the railroad using yellow hammers
and set up residency in Wilmington. They bred within the family and became mutant from insest.