Building an ADU in Illinois

Illinois has no statewide ADU law

No Illinois law makes cities, villages or counties allow ADUs. Your local zoning code decides whether you can add a coach house, an attic or basement unit, or a backyard cottage, and on what terms.

State law gives a city's or village's corporate authorities the power "to regulate and limit the height and bulk of buildings," to set building and setback lines, to regulate "the intensity of the use of lot areas," and to divide the city into zoning districts and restrict uses in each. Those general zoning powers are where local ADU rules come from.

Outside city and village limits, the county board zones land, except where a city, village or incorporated town has its own zoning ordinance. If you live in an unincorporated area, start with your county's zoning office. [1][2][4][7]

Home rule: why rules vary so much

Under the Illinois Constitution, a county with an elected chief executive officer and any municipality with more than 25,000 people is a home rule unit. Smaller municipalities can become home rule units by referendum, and a home rule unit can vote by referendum to give up that status. A home rule unit "may exercise any power and perform any function pertaining to its government and affairs," including regulating for public health, safety and welfare.

Home rule units share powers with the state unless the General Assembly "by law" specifically limits them. The statewide ADU bills filed in 2025 and 2026 (HB 1813, HB 1709, SB 3726, SB 4071 and HB 5626) each said it "limits home rule powers." None passed, so home rule cities still write their own ADU rules. [1][2][3][8][9][10]

The 2026 ADU bills that stalled

Two 2026 bills would have required ADUs statewide. They did not pass, and neither did the Senate's broader middle housing bill:

• SB 4071 (Sen. Robert Martwick), filed February 24, 2026, would have required every municipality, starting January 1, 2027, to permit ADUs "in all zoning districts that permit single-family dwellings" without extra rules on lot size, setbacks, design review or space limits. It would also have barred extra parking, rules requiring a family relationship between the ADU and main-house occupants, and minimum or maximum ADU square footage. It was referred to the Senate Assignments Committee and went no further.
• HB 5626 (Rep. Kam Buckner), filed February 18, 2026, had the same ADU rule plus middle housing (up to 4, 6 or 8 units depending on lot size), third-party plan review if cities miss review deadlines, and a ban on parking minimums for homes under 1,500 sq ft starting January 1, 2027. Its last action was a referral to the House Rules Committee.
• SB 640, the Senate's middle housing vehicle, got committee approval of a floor amendment in May 2026 but was never called for a final vote. On June 1, 2026 it was re-referred to the Senate Assignments Committee.

None of these rules apply to your city unless a future law enacts them. [1][2][11][12]

Earlier and other ADU bills

Several narrower bills would have stopped local governments from banning ADUs outright, while still allowing "reasonable regulations relating to the size and location" of ADUs:

• HB 1813 (2025) passed the House Housing Committee 18-0 on March 20, 2025, but was re-referred to the Rules Committee on April 11, 2025.
• HB 1709 (2025), the proposed Local Accessory Dwelling Unit Act, was re-referred to the Rules Committee on March 21, 2025.
• SB 3726 (2026), a Senate version of the same idea, was re-referred to Assignments on April 24, 2026.

HB 5791 (filed May 2026), the proposed Family First Housing Act, would allow one ADU on an owner-occupied lot for a parent of the owner or the owner's spouse. It was referred to the House Rules Committee on May 26, 2026. [3][9][10][13]

Parking near transit: the People Over Parking Act

The People Over Parking Act (Public Act 104-0457, from SB 2111) took effect June 1, 2026. It says a unit of local government "may not impose or enforce any minimum automobile parking requirements" on a development project located within one-half mile of a public transportation hub or one-eighth mile of a public transportation corridor.

• A public transportation hub is a rail transit station, a boat or ferry terminal served by bus or rail, or an intersection of two or more bus routes with a combined frequency of 15 minutes or less during morning and afternoon peak commute periods.
• A public transportation corridor is a street with bus service at that same 15-minute combined frequency during peak periods.
• A development project includes a project involving a permit for construction or reconstruction.

If you choose to build parking, the local government can still set rules for it, such as car-share or shared spaces, but can't require it to be free. The act applies to home rule units too. A 2026 bill to limit the act to cities over 2,000,000 people (HB 4588) was re-referred to the House Rules Committee in March 2026. Ask your city how it applies the act to an ADU on your lot. [5][6][14]

Family-only rules and other local limits

Illinois zoning law lets a city "classify, to regulate and restrict the use of property on the basis of family relationship." The 2026 bill that would have barred cities from requiring a family relationship between the people in an ADU and the main house (SB 4071) did not pass. Check your city's code for any rule on who may live in an ADU before you plan to rent it.

State zoning law also lets cities "fix standards to which buildings or structures therein shall conform" and prevent additions, alterations or remodeling of existing buildings that would avoid zoning limits. Before you convert an attic, basement or garage into a unit, ask your local zoning office what approvals you need. [2][4]

Where local rules differ

Because the rules are local, ask your city or county zoning office:

• Which zoning districts allow an ADU, coach house or conversion unit.
• The maximum size, height and setbacks.
• Whether the owner must live on the property, and who may live in the ADU.
• How many parking spaces you need, and whether the People Over Parking Act removes that requirement on your lot.
• Whether you can rent the ADU short term.
• The permit, plan review and utility connection fees.

Chicago, for example, adopted an Additional Dwelling Units ordinance in 2020 with five pilot areas, and the City Council voted in September 2025 to expand it beyond the pilot program. See our Chicago ADU guide. Our ADU permit process guide, garage conversion guide and ADU cost guide cover the general steps. [4][5][15]

Illinois laws to know

• Illinois Municipal Code, 65 ILCS 5/11-13-1

  Gives cities and villages the power to regulate building height and bulk, setbacks, lot use, zoning districts and uses, which is where local ADU rules come from. [4]

• Counties Code, 55 ILCS 5/5-12001

  Lets county boards zone land outside cities, villages and towns that have their own zoning, so county rules govern ADUs in those unincorporated areas. [7]

• People Over Parking Act, Public Act 104-0457 (SB 2111, 2025)

  Since June 1, 2026, bars local governments, including home rule units, from imposing minimum parking requirements on development projects near frequent transit. [5][6]

• HB 5626 and SB 4071 (2026), proposed ADU law (not passed)

  Would have required municipalities to allow ADUs in all zoning districts that permit single-family homes; both bills stalled in committee. [1][2]

Questions people ask