ADU Laws in Illinois (2026)
Illinois state ADU law details, key provisions, preemption status, and recent legislative changes for accessory dwelling units.
Law Name
State ADU Law
Preempts Local Ordinances
No — local rules may be stricter
Has State Law
Yes
Key Provisions
No statewide ADU preemption or mandate law exists in Illinois as of 2026
ADU regulation is left entirely to local municipalities under Illinois Municipal Code (65 ILCS 5)
Chicago enacted its own ADU Ordinance (2020, expanded 2022) allowing both attached and detached ADUs citywide
Evanston, Oak Park, and other suburban municipalities have adopted their own ADU-permissive ordinances
Illinois has no statewide housing compact or state-mandated zoning reform
Legislative History
2020 — Chicago ADU Ordinance O2020-5816
Chicago (local, not state law) enacted ADU Ordinance allowing coach houses and basement apartments in 5 pilot areas
2022 — Chicago ADU Ordinance Expansion O2022-1679
Chicago (local, not state law) expanded ADU Ordinance to all city neighborhoods, allowing both attached and detached ADUs citywide with owner-occupancy requirement
Official Sources
Source: Illinois State ADU Law. Last verified April 3, 2026. View source