I like a good bushcraft knife, which can sometimes bump up against legal limits in certain places. Bushcraft knives tend to be on the longer side.

• Illinois state
  • unlimited, unless when on building or land supported (even partially) with "public funds", then it's limited to 3 inches
  • list of knife-related statutes
  • analysis by [ostensibly competent] lawyers: [1]
  • 720 ILCS 5/21-6 reads "Whoever possesses or stores any weapon enumerated in Section 33A-1 in any building or on land supported in whole or in part with public funds... commits a Class A misdemeanor."
• Chicago
  • limited to 2.5" in some (all?) places
  • analysis by [ostensibly competent] lawyers: [1]
  • list of knife-related statutes:
    • 8-24-005 — Definitions
    • 8-24-020 — Sale or possession of deadly weapons.
    • 8-24-021 — Sale, display and use of utility knives.