In plain words

Illinois has no statewide law about accessory dwelling units (ADUs). An ADU is a small second home on the same lot as a house. It might be a basement apartment, an attached suite, or a backyard cottage, which Chicago calls a coach house. Because the state is silent, each city, village and county decides through its zoning. Zoning is the local rulebook for what can be built where. Some towns allow ADUs. Many suburbs still do not, or allow them only for relatives.

Chicago now allows ADUs in many neighborhoods. In September 2025 the City Council voted to expand them beyond a five-area pilot, starting April 1, 2026. In many single-family areas, the local alderperson (city council member) has to opt a block in first. Evanston allows one ADU on any residential lot that meets its rules.

One state law does touch ADUs. Since June 1, 2026, towns generally cannot require parking spaces for new homes, including ADUs, close to train stations or frequent bus lines.

State lawmakers have tried to go further. In 2026 the governor's BUILD plan included Senate Bill 4071 and House Bill 5626. They would make every city allow an ADU wherever a single-family home is allowed. Towns could not demand extra parking or cap ADU size. Neither bill got a vote in the spring 2026 session. Narrower bills from 2023 through 2026 also stalled. They could still move before the current legislature ends in January 2027.

For now, your town's code is what counts. You may be able to build an ADU if local rules and your property allow it. Call your local zoning office before you pay for a design.

The rules at a glance

State ADU lawNo. Each city, town or county decides.
Owner living on siteTowns may require the owner to live on the property.
ParkingNo ADU-specific state rule. But the People Over Parking Act (50 ILCS 845, Public Act 104-0457, signed December 16, 2025, effective June 1, 2026) bars cities, villages and counties from requiring minimum off-street parking for development projects, including new homes, within half a mile of a rail station or other public transportation hub, or one-eighth of a mile of a bus corridor with service every 15 minutes or better at peak times. ADUs in those areas fall under it. Elsewhere each town sets its own rule; Chicago's 2025 ordinance and Evanston's 2020 ordinance both require no extra parking space for an ADU.
SizeState law doesn’t set this. Local caps vary: Evanston caps most ADUs at 1,000 sq ft; CMAP's 2023 comparison table lists Park Forest at 40% of the house's floor area or 800 sq ft and Bull Valley at 30% of the house; Chicago limits a coach house's floor area to 60% of the required rear setback area (about 450 sq ft on a standard lot).
Lot size and setbacksState law doesn’t set this. Lot size, yard and setback limits come from each municipality's or county's zoning code.
FeesState law doesn’t set this.
Short-term rentalsState law doesn’t set this. Rental rules, including short-term rental bans or licensing, are set locally.

What to do next

  1. Find out who zones your land: your city or village if you live inside one, or your county if you live in an unincorporated area.
  2. Ask the zoning office whether ADUs, coach houses, in-law suites or accessory apartments are allowed in your zone, and whether approval needs a public hearing, special use or variance.
  3. Write down the local limits before you design: who may live in the unit (some towns allow relatives only), whether the owner must live on site, size, height, setbacks and parking. If you are near a train station or a frequent bus line, ask whether the state People Over Parking Act removes the parking requirement.
  4. In Chicago, check whether your block is in an ADU-allowed area and start the city's ADU pre-certification before hiring a designer.
  5. Check your HOA covenants and deed; local approval does not cancel private restrictions.
  6. Follow SB 4071 and HB 5626 on ilga.gov; bills not passed by January 2027 must be refiled in the next General Assembly.

What your town still decides

Cities and villages zone under the Illinois Municipal Code, and counties zone unincorporated land. Any city over 25,000 people (and any county with an elected chief executive) is a home-rule unit under Article VII, Section 6 of the state constitution, which gives it broad power to set its own rules; smaller towns can become home rule by referendum. No state statute requires any of them to allow ADUs, so the answer depends on the town. Many suburbs still ban ADUs or limit them to relatives, and some require the owner to live on site. The regional planning agency CMAP counted only 12 northeastern Illinois communities with ADU rules in May 2023 (Antioch, Bull Valley, Chicago, Evanston, Homewood, Lake Bluff, Northbrook, Oak Park, Park Forest, South Elgin, Wilmette and Woodstock). CMAP has not updated that list since, and it covers only the Chicago region; downstate cities such as Champaign (2022) and Moline (2024) also have ADU rules. Most of the pending state ADU bills state that they limit home rule powers, which is how they would override local codes if passed. The Illinois Municipal League opposes the 2026 BUILD bills as preemption of local control.

Examples of local rules

  • Chicago: The City Council first allowed ADUs in five pilot areas in 2020 (in effect May 1, 2021). In September 2025 it voted to expand them (ordinance SO2024-0008918, passed 46-0 on September 25, 2025), effective April 1, 2026. ADUs (basement or attic 'conversion units' and backyard 'coach houses') are now allowed in multi-unit, business and commercial zones. In single-family (RS) zones, they are allowed only inside the old pilot areas and in blocks an alderperson (city council member) has opted in by ordinance; ordinances passed December 10, 2025 and February 18, 2026 redrew those opt-in areas before the April start. No extra parking is required. The West, South and Southeast pilot areas keep an owner-occupancy rule for houses with one to three units and a yearly cap on ADU permits per block. Properties that add two or more ADUs must rent half of them at affordable rents, and these ADUs cannot be used as short-term rentals. The city runs an ADU pre-certification process before the building permit. Source
  • Evanston: Ordinance 86-O-20 (2020) allows one ADU on any residential lot by right, either inside or attached to the home or in a detached building, but not both. ADUs are capped at 1,000 sq ft (larger only inside an existing floor that is already bigger), detached ones at two stories. No parking is required for the ADU. The owner does not have to live on site, but the ADU cannot be sold separately. Owners must register the unit and pass a city inspection before renting it. Source
  • Northeastern Illinois suburbs (CMAP survey): The Chicago Metropolitan Agency for Planning's ADU guide (May 12, 2023) lists 12 communities in the region with ADU codes and says nearly a dozen towns permit ADUs or are considering it. Its comparison shows common local limits: some towns require the owner to live on site, some allow only family members in the ADU, some require a parking space, and size caps are often tied to the main house. The list has not been updated since 2023. Source

What we’re still confirming

  • Two bills that would make every town allow one ADU per single-family home, SB 4071 and HB 5626, are still pending and could come up in the fall 2026 veto session or in January 2027.
  • Confirm Chicago's details, such as which areas allow ADUs, owner-occupancy rules in former pilot areas and coach-house size, in the city's zoning ordinance.

Laws, bills and citations

Proposed and failed bills (8). None of these is law.
  • SB 4071 (104th GA, 2025-2026): in committee as of October 3, 2026. Part of Gov. Pritzker's BUILD housing plan. Starting January 1, 2027, every municipality would have to allow one ADU per single-family home in every zone that allows single-family homes, with no extra lot size, setback, design, parking or size limits beyond what applies to the house itself. Towns could not require occupants to be related. Filed February 24, 2026 and still in the Senate Assignments Committee; no committee or floor vote has been recorded (last action: a co-sponsor added March 13, 2026). Bill page
  • SB 3726 (104th GA, 2025-2026): in committee as of October 3, 2026. Filed February 5, 2026 by Sen. Steve Stadelman. Like HB 1813, it would bar municipalities from prohibiting ADUs while letting them set reasonable size and location rules like those for other accessory buildings. Assigned to the Senate Executive Committee, then sent back to the Assignments Committee on April 24, 2026 under the committee deadline rule, with no vote. Bill page
  • HB 5626 (104th GA, 2025-2026): in committee as of October 3, 2026. The House omnibus version of BUILD. It combines the statewide ADU rule with up to 4-8 homes per lot depending on lot size, limits on parking minimums from 2027, statewide impact-fee formulas, permit review deadlines with third-party reviewers, and single-stair buildings. Filed February 18, 2026 and still in the House Rules Committee (last action: a co-sponsor added June 22, 2026). Bill page
  • HB 1813 (104th GA, 2025-2026): in committee as of October 3, 2026. Would bar municipalities from prohibiting ADUs while letting them set reasonable size and location rules like those for other accessory buildings. Passed the House Housing Committee 18-0 on March 20, 2025, then stalled on second reading and was sent back to the Rules Committee on April 11, 2025. Bill page
  • HB 1709 (104th GA, 2025-2026): in committee as of October 3, 2026. Rep. Kam Buckner's refiled Local Accessory Dwelling Unit Act (same text as HB 4213 from 2023). It would bar cities and counties from prohibiting ADUs while allowing reasonable size and location rules. Filed January 24, 2025, assigned to the House Cities and Villages Committee, and sent back to the Rules Committee on March 21, 2025 with no vote. Bill page
  • HB 3552 (104th GA, 2025-2026): in committee as of October 3, 2026. The Local Accessory Dwelling Unit Act. It would require cities and counties to approve ADU permits by right within 60 days (or the permit is deemed approved), ban parking mandates and fees beyond permit review, and stop denials over unrelated old code problems on the lot. Assigned to the House Housing Committee, then sent back to the House Rules Committee on March 21, 2025 with no vote. Bill page
  • HB 5791 (104th GA, 2025-2026): in committee as of October 3, 2026. The Family First Housing Act. It would let an owner-occupied home have one ADU for a parent of the owner or of the owner's spouse, starting January 1, 2027. Filed May 25, 2026 and referred to the House Rules Committee. Bill page
  • HB 4213 (103rd GA, 2023-2024): died as of October 3, 2026. An earlier Local Accessory Dwelling Unit Act, filed November 2, 2023 by Rep. Kam Buckner, that would have stopped local governments from banning ADUs. It was sent back to the Rules Committee on April 5, 2024 and died when the 103rd General Assembly ended on January 7, 2025. Buckner refiled the same text as HB 1709 and an expanded version as HB 3552. Bill page

Sources

  1. ILGA bill status: SB 4071 (Muni Cd-Accessory Dwellings), 104th GA · official source · checked 2026-10-03
  2. ILGA bill status: HB 5626 (BUILD omnibus), 104th GA · official source · checked 2026-10-03
  3. ILGA bill status: HB 1813, 104th GA · official source · checked 2026-10-03
  4. ILGA bill status: HB 3552 (Local Accessory Dwelling Unit Act), 104th GA · official source · checked 2026-10-03
  5. ILGA bill status: HB 5791 (Family First Housing Act), 104th GA · official source · checked 2026-10-03
  6. HB 4213 as introduced, 103rd GA (ILGA PDF) · official source · checked 2026-10-03
  7. ILGA bill status: HB 4213, 103rd GA (session sine die January 7, 2025) · official source · checked 2026-10-03
  8. ILGA bill status: SB 3726 (Muni Cd-Accessory Dwellings), 104th GA · official source · checked 2026-10-03
  9. ILGA bill status: HB 1709 (Local-Accessory Dwelling Units), 104th GA · official source · checked 2026-10-03
  10. ILGA bill status: SB 2111, Public Act 104-0457 (creates the People Over Parking Act; signed Dec. 16, 2025; effective June 1, 2026) · official source · checked 2026-10-03
  11. Public Act 104-0543 (amends People Over Parking Act definitions, 50 ILCS 845/5-5) · official source · checked 2026-10-03
  12. ILGA public acts of the 104th General Assembly (index used for full-text search) · official source · checked 2026-10-03
  13. 65 ILCS 5/ Illinois Municipal Code · official source · checked 2026-10-03
  14. Illinois Constitution, Article VII (home rule units, Section 6) · official source · checked 2026-10-03
  15. City of Chicago Department of Housing: Additional Dwelling Unit (ADU) Program · official source · checked 2026-10-03
  16. City of Evanston: Ordinance 86-O-20 staff memo (ADU regulations) · official source · checked 2026-10-03
  17. City of Evanston: Exploring Accessory Dwelling Units · official source · checked 2026-10-03
  18. CMAP: What your community needs to know about accessory dwelling units (May 12, 2023) · checked 2026-10-03
  19. Illinois Municipal League: Zoning preemptions among Governor's BUILD bills (April 24, 2026) · checked 2026-10-03
  20. Capitol News Illinois: Despite BUILD's failure, housing advocates celebrate legislative wins (June 12, 2026) · checked 2026-10-03
  21. Housing Action Illinois: 2026 State Legislative Session Wrap-Up · checked 2026-10-03
  22. Abundant Housing Illinois: Chicago ADU FAQ (ordinance SO2024-0008918) · checked 2026-10-03
  23. Chicago Cityscape: Build an ADU in Chicago · checked 2026-10-03
  24. Chicago Cityscape: Build an ADU in Illinois (municipal ADU table) · checked 2026-10-03

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.