Illinois ADU Laws & Permit Guide (2026)
Illinois ADU rules are set at the city and county level with no statewide preemption. Chicago's Missing Middle Housing Ordinance (2021) is the most significant ADU policy in the state. Suburban Chicago and other cities have varying policies.
Illinois ADU At a Glance
Permit Timeline
90–150 days
Average Build Cost
$110,000 – $280,000
Maximum Size
Varies by city (Chicago: up to 1,000 sq ft in pilot areas)
Owner-Occupancy Required
Required in Chicago ADU pilot program
Impact Fees
Varies by municipality
Setbacks
Varies; Chicago typically 2 ft rear, 2 ft side
Recent Law Changes in Illinois
Established an ADU pilot program in five Chicago wards, allowing coach houses, garage conversions, and interior conversions to be permitted more easily. Owner-occupancy required. The program has since been expanded.
Chicago expanded the ADU pilot program to additional wards citywide, making more Chicago homeowners eligible to build accessory dwelling units.
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Browse Illinois Contractors →Frequently Asked Questions — ADUs in Illinois
Can I build an ADU in Chicago?
Possibly yes. Chicago's ADU pilot program allows coach houses, garage conversions, and interior conversions in eligible wards. Owner-occupancy is required. Check Chicago's ADU program page to confirm whether your address falls within the program area.
How much does it cost to build an ADU in Chicago?
Chicago ADU costs typically range from $110,000 to $280,000 for a detached coach house or garage conversion. Chicago's high union labor costs make it one of the more expensive Midwest markets. Interior basement conversions can be less — often $50,000–$120,000.
Do I have to live on my property to have an ADU in Chicago?
Yes. Chicago's ADU pilot program requires owner-occupancy — you must live in the primary residence on the property. This is different from many other states and cities that have eliminated owner-occupancy requirements.
Are ADUs allowed in suburban Chicago?
ADU rules in suburban Cook County and other collar counties vary widely by municipality. Evanston, Oak Park, and some other suburbs have ADU programs. Many suburban municipalities do not allow ADUs or have very restrictive ordinances. Check with your local planning department.
How long does ADU permitting take in Chicago?
Chicago's Department of Buildings typically processes ADU permits in 90–150 days. The city has been working to streamline ADU permitting under the pilot program, and pre-approved plan sets are available for some ADU types.
Sources
Disclaimer: The information on this page is provided for general informational purposes only and does not constitute legal, financial, or construction advice. ADU regulations change frequently — always verify current rules with your local planning department and consult a licensed professional before making decisions. ADUHomeResource.com is not liable for any errors, omissions, or outcomes resulting from use of this information.