DuPage County, IL Accessory Structures: ADU Rules (2026)
ADU rules in DuPage County, IL, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Max ADU size
- 1,000 square feet
- Approval needed
- Conditional use + building permit
- Combined occupancy cap
- 5 people
- Vehicle cap
- 6 passenger vehicles
- Minimum lease term
- 6 months
Summary
DuPage County allows one accessory dwelling unit per single-family lot, but only as a conditional use capped at 1,000 square feet and gated behind a County Board-approved permit.
An accessory unit may be maintained as part of the principal single-family dwelling as a conditional use in the districts hereinafter indicated. A. Only one (1) accessory dwelling unit may be maintained in a converted dwelling or on a property where there is an existing dwelling unit. B. The total floor area of an accessory dwelling unit shall not exceed one thousand (1,000) square feet.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 14 Update 1).
Full Breakdown
Homeowners in unincorporated DuPage County can convert part of a single-family home into an accessory dwelling unit only after winning a conditional-use permit from the County Board. The ADU is capped at 1,000 square feet, must meet the same yard and bulk standards as the principal or accessory building, and needs a building permit with a reconversion plan on file. Combined occupancy across both units is capped at five people, total vehicles at six, and the ADU can't be leased for stints shorter than six months. At least one owner must live on site, and the conditional use itself expires automatically if any requirement lapses.
Violations & Fines
The County Development Committee enforces the permit; building without one, exceeding 1,000 sq ft, or leasing under six months voids the conditional use, forcing reconversion to a single-family dwelling within 90 days.
Frequently Asked Questions
Can I build a detached ADU in unincorporated DuPage County?
Do I need County Board approval for an ADU?
Sources & Official References
Other rules in DuPage County
How DuPage County compares: Easiest Cities to Build an ADU·Compare DuPage County to another location·View the Illinois accessory structures overview
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