south of 80 Share definition Flag The term south of 80 refers to people who live south of I-80 in Illinois. Known to be very dumb witted and inbred. “Wow that Jim guy is dumber than a brick.” “That’s because he lives south of 80” south of 80 by North of 80 guy February 9, 2021 0 0 Get merch Get the south of 80 mug. Buy Now — $32.95 See more merch