Inbred Humboldt

Humboldt County has been named the "most inbred county in the country", according to this Craigslist ad. I had no idea!

"The root cause of the inbreeding is fear of outsiders. Our county government works relentlessly to keep new people from moving to Humboldt. Several local businesses are afraid new people will bring new competition. Virtually all of our local officials are closely related." 

Can this be true??? A guy told a joke on my online game, Aces High, a year or two ago:

"If mom and dad get divorced, does that mean they're still considered brother and sister?". Might that actually be a Humboldt joke?