Chicago's gang population is difficult to gauge the size. The information have varied but I think this list is half or so inaccurate on total membership. This covers the Chicagoland in Cook County. Most recent reports states the estimate is around 70,000 in the city. Yet the national gang report place Cook County around 60,000+.

A 1993 Chicago Tribune report that the gang population was around 38,000 with half of that membership in 4 mobs ( GD, VL, LK , & LD).
Im leaning more in between the 60-70K mark.