Green’s Dictionary of Slang

1. (US Und.) of a fellow criminal, acceptable, trustworthy [Chicago’s association with gangster Al Capone].

1950

Goldin et al. DAUL 74/2: From Chicago. Okay. [Note: Usually applied to an out-of-towner whose reputation is satisfactory in the underworld.] ‘Meet Mike the Mooch, boys; he’s from Chicago.’.

2. (US campus) unaware of what’s going on, behaving like an ‘air-head’ [play on Chicago as the Windy City n. (1)].

1985

Eble Campus Sl. Oct. 4: from Chicago – spaced out.