An Illinois resident who lives in the lower 3/4 of the state - anywhere south of Chicagoland.
"Where are you from?"
"Chicago, what about you?"
"I'm from Dwight."
"Oh, you're a downstater."
"No - Dwight is pretty far north. It's only an hour south of Chicago."
"Hey, if you're farther than Joliet, you're a downstater."