Straight answers

Are tiny homes legal in Illinois, and where can you put one?

Yes on a foundation, wherever the city or county zoning allows a house or a backyard unit that small. Illinois decides less at the state level than most summaries claim. There is no single statewide building code for houses. A city or county chooses whether to adopt one, and since 1 January 2025 a local code must regulate structural design at least as stringently as a baseline edition of the International Residential Code. Where no code has been adopted, state law writes one into the construction contract. No state law makes a city allow a backyard home, although bills to do that were filed in 2026. The state does regulate two things directly: the energy code, which applies statewide, and homes built in a factory, which need Department of Public Health approval and the Illinois seal. A tiny home on wheels is a house trailer in the vehicle code, and where one may be lived in is a local question.

Figures verified against the sources below · October 9, 2026

01 — The longer answer

What Illinois decides, and what your city or county decides

Illinois has no single statewide building code for houses

Two descriptions of Illinois circulate, and both are wrong. One says the state has no building codes. The other says a 2025 law made every area adopt one. The Capital Development Board Act says something in between. Beginning 1 January 2025, any municipal or county building code must regulate the structural design of residential buildings in a manner at least as stringent as the baseline residential code. The baseline is the edition of the International Residential Code, first published in the current year or the preceding nine calendar years, with the least restrictive provisions for structural design. Structural design means the capacity of the building and its foundation to withstand loads such as snow, wind, soil and earthquake, and to resist flood damage. So the edition in force can differ from one town to the next, but a local code cannot fall below that structural floor. The Capital Development Board publishes a directory of the codes that cities and counties have reported to it.

Building where no code has been adopted

The same Act still defines a non-building code jurisdiction: any area where the municipality or county has not adopted a building code. For a new house there, the Illinois Residential Building Code Act applies. The contract to build must adopt a residential building code that the home builder and the home purchaser agree on. They may choose the International Residential Code, in its current or most recent preceding edition, or any municipal or county residential code in effect within 100 miles of the new home. If they do not agree, or the contract names no code, the current edition of the International Residential Code becomes part of the contract by law, along with the state energy code and the Illinois Plumbing Code. A builder who constructs a home for resale must certify to the buyer which code the home was built to. This is a contract rule. The statutes we read do not create a state inspection of houses in those areas, so the code named in your contract is the standard your builder answers to.

The energy code applies everywhere in Illinois

The Energy Efficient Building Act works differently from the building code. The Capital Development Board adopts the latest International Energy Conservation Code with Illinois amendments, and for residential buildings the Act makes it both the minimum and the maximum. The board states that the 2024 edition, as amended, went into effect on 30 November 2025. A local government that does not regulate energy standards does not have to administer the code, but construction there is still subject to the Act. For houses, a local government may not regulate energy standards either less or more stringently than the state. The statute lists the exceptions that may be stricter: a municipality of 1,000,000 or more people, a municipality that has adopted the Illinois Stretch Energy Code, and a local government that already had equivalent or stricter standards by 15 May 2009.

Is there a minimum size for a house in Illinois?

The state statutes we read set none. Where a minimum exists, it comes from local zoning. The Municipal Code gives each municipality the power to regulate the height and bulk of buildings and the intensity of the use of lot areas, and to divide its territory into districts. The Counties Code gives a county board the power to regulate the location and use of buildings and land outside municipalities that have their own zoning. A minimum floor area in a zoning ordinance is an exercise of those powers and differs from place to place. The residential code's tiny house appendix, written for houses of 400 square feet or less, applies in Illinois only where a city or county has adopted it. We did not find a state list of which have.

No state law makes a city allow a backyard home

Illinois has no accessory dwelling unit statute. Bills to create one were filed in the 2026 session. Senate Bill 4071 would have each municipality, from 1 January 2027, permit accessory dwelling units in every zoning district that permits single-family dwellings. Senate Bill 3726 and House Bill 5626 take up the same subject. When we read the General Assembly's status pages, none of the three had been voted on in either chamber: the House bill was in the Rules Committee and both Senate bills were with the Committee on Assignments. Until one becomes law, whether a second home may stand behind a house is written in the local zoning ordinance.

A factory-built tiny home needs the Illinois seal

A home built in a factory for a site in Illinois falls under the Illinois Modular Dwelling and Mobile Structure Safety Act, which the Department of Public Health administers. A modular dwelling is a building of closed construction, made by a manufacturer on or off the building site, and installed on an approved foundation and support system. No one may sell one, or offer one for sale, for location in Illinois unless it bears a seal issued by the Department and the manufacturer's certification that it complies with the state safety code. Under the Department's rules a manufacturer must obtain written approval for each model before building it, and an approved inspection agency labels the finished unit before it leaves the plant. A unit sealed by a state with a reciprocity agreement is the one stated exception. The approved foundation is a closed perimeter of materials such as concrete, masonry, steel or treated lumber that extends into the ground below the frost line. State law also says that, unlike with manufactured homes, the local building official may require items beyond the state minimum. Ask any manufacturer, ours included, whether the model you want has Department approval and will carry the Illinois seal.

A tiny house on wheels is a house trailer

The Illinois Vehicle Code defines a house trailer as a trailer or semitrailer equipped and used for living quarters or for human habitation, temporarily or permanently. A travel trailer is a trailer designed to provide living quarters for recreational, camping or travel use, of a size or weight that needs no overdimension permit when towed. Those definitions are about registration and the road. They do not say where a unit may be parked and lived in. On construction, the Department of Public Health's guide to factory-built housing, dated 2007, states that neither the state nor the federal government regulates the construction of recreational vehicles. A county board may regulate camps and parks that accommodate people in house trailers, and may prohibit residential use of structures that do not meet its building rules.

Chicago: coach houses and where they are allowed

Chicago calls a detached backyard home a coach house and a unit inside the existing building a conversion unit. The City Council first approved its Additional Dwelling Units ordinance in 2020 for five pilot areas, and voted in September 2025 to expand it. The City now allows these units by right in all multi-unit residential districts and in certain business and commercial districts. In the single-family districts, RS1 to RS3, one is allowed only inside an area the Council has designated by ordinance. Some of those areas cap how many units can be approved on a block each year, and some require the owner to live in the main house. One coach house is allowed per property and it can be built only after the main building. No extra parking is required, and short-term rentals are not permitted in a coach house built after 2021. A general contractor building one must take part in a registered apprenticeship program. Every project needs a pre-certification from the Department of Housing and then building permits. Chicago's rules are no guide to any suburb.

Unincorporated land and farms

Outside city limits the county is the regulator, and the Counties Code limits what it may do on working farmland. County building regulations do not reach buildings for agricultural purposes on farms, farm residences included. County zoning may not impose regulations or require permits on land where agriculture is the principal activity, although buildings there can be held to setback lines, a county may set a minimum lot size for residences on agricultural land, and small parcels in the largest counties are treated differently. None of this helps on a residential lot. The exemption turns on farming being the main use of the land.

Can you live in a tiny home full time in Illinois?

In one built as a house, yes, where the zoning allows that house. A home on a permanent foundation, built to the local code or to the code named in the contract, is a dwelling. So is a modular dwelling carrying the Illinois seal on an approved foundation. A home that stays on its wheels is the hard case. State law classes it as a trailer and leaves where it may be occupied to each city and county. We did not read county or suburban ordinances for this page, so ask the zoning office directly whether a unit on wheels may be lived in on your lot, and for how long.

Lists of which Illinois counties allow tiny homes circulate widely. The state sources we read publish no such list and leave land use to each city and county, so the rule for your land is in your own zoning ordinance. The Illinois guide carries the code position and the energy code, with the source for each statement.

02 — Where to go next

The Illinois state guide Where a tiny home can go in the US Building codes, state by state How certification works

03 — Sources

Each figure above links to the authority it came from.

20 ILCS 3105/10.18(e): beginning January 1, 2025, any municipal building code or county building code must regulate the structural design of residential buildings in a manner that is at least as stringent as the baseline residential code; baseline residential code means the edition of the International Residential Code for One- and Two-Family Dwellings first published by the International Code Council during the current year or preceding 9 calendar years with the least restrictive provisions for structural design; structural design means the capacity of a structure, including its foundation, to withstand dead, live, snow, wind, soil, rain and earthquake loads and to resist flood damage. 10.18(c): the Board must identify each municipality's and county's adopted model code on its public website
ilga.gov
20 ILCS 3105/10.09-1: non-building code jurisdiction means any area of the State in a municipality or county that has not adopted a building code or has not identified its adopted code to the Board; subsection (e): except as provided in Section 15 of the Illinois Residential Building Code Act, new residential construction is exempt from this Section
ilga.gov
815 ILCS 670/10, 670/15 and 670/20, Illinois Residential Building Code Act: International Residential Code means the current edition or the most recent preceding edition, excluding Parts IV and VII; a contract to build new residential construction in any non-building code jurisdiction must adopt a residential building code agreed to by the home builder and the home purchaser, who may agree to the International Residential Code or any municipal or county residential building code in effect on the first day of construction within 100 miles of the new home; if they fail to agree or no code is stated, the energy code, the plumbing code and the current edition of the International Residential Code shall, by law, be adopted as part of the construction contract; a builder constructing a home for resale must certify the code to the buyer
ilga.gov
Illinois Capital Development Board, Building Codes and Regulations: lists separate requirements for residential buildings in jurisdictions that have not adopted a building code and in jurisdictions that have; starting 1/1/25 local codes must regulate the structural design in a manner at least as stringent as the IRC; links the Illinois Municipal Code Directory
cdb.illinois.gov
20 ILCS 3125/15: the Board shall adopt the Code as the minimum and maximum requirements for residential buildings in the State, except as provided in Section 45. 3125/20(d): a unit of local government that does not regulate energy efficient building standards is not required to adopt, enforce, or administer the Code; construction there is subject to the provisions of the Act
ilga.gov
20 ILCS 3125/45(b): no unit of local government, including any home rule unit, may regulate energy efficient building standards for residential buildings in a manner that is either less or more stringent than the standards established pursuant to the Act, except that units that adopted equivalent or more stringent standards on or before May 15, 2009, a municipality that has adopted the Illinois Stretch Energy Code, and a municipality with a population of 1,000,000 or more may be more stringent
ilga.gov
Illinois Capital Development Board, Illinois Energy Conservation Code: the 2024 edition of the IECC as amended went into effect on 11/30/25
cdb.illinois.gov
65 ILCS 5/11-13-1: the corporate authorities in each municipality have the power to regulate and limit the height and bulk of buildings, to regulate and limit the intensity of the use of lot areas, and to divide the municipality into districts
ilga.gov
55 ILCS 5/5-12001: the county board has the power to regulate and restrict the location and use of buildings, structures and land outside the limits of cities, villages and incorporated towns which have in effect municipal zoning ordinances; the powers shall not be exercised so as to impose regulations or require permits with respect to land used for agricultural purposes when such purposes constitute the principal activity on the land, other than certain parcels of less than 5 acres in counties above stated populations, except that buildings for agricultural purposes may be required to conform to building or setback lines and counties may establish a minimum lot size for residences on land used for agricultural purposes
ilga.gov
55 ILCS 5/5-1063: a county board may prescribe rules governing the construction and alteration of all buildings, structures and camps or parks accommodating persons in house trailers, house cars, cabins or tents outside the limits of cities, villages and incorporated towns, excluding those for agricultural purposes on farms including farm residences, and may prohibit the use for residential purposes of buildings and structures which do not comply
ilga.gov
Illinois General Assembly, bill status for SB 4071 (104th General Assembly): amends the Illinois Municipal Code to provide that, beginning January 1, 2027, each municipality shall permit accessory dwelling units in all zoning districts that permit single-family dwellings; filed and referred to Assignments on 24 February 2026, with no committee vote or floor action recorded (as read 9 October 2026). The status files for SB 3726 (re-referred to Assignments 24 April 2026) and HB 5626 (referred to Rules Committee 19 February 2026) show the same
ilga.gov
430 ILCS 115/2: modular dwelling means a building assembly designed for habitation as a dwelling, of closed construction, made or assembled by a manufacturer on or off the building site and installed on an approved foundation and support system; the construction of modular dwelling units located in Illinois is regulated by the Illinois Department of Public Health; approved foundation and support system means a closed perimeter formation of materials such as concrete, mortared concrete block, mortared brick, steel, or treated lumber extending into the ground below the frost line; mobile structure excludes recreational vehicles and single family residences
ilga.gov
430 ILCS 115/4(a): no person may rent, sell, or offer for sale to anyone within this State any modular dwelling or mobile structure unless it bears a seal issued by the Department and a certification by the manufacturer that it complies with the applicable safety code
ilga.gov
77 Ill. Adm. Code 880.20(a) and 880.30(a): all manufacturers must obtain written approval from the Department for each model to be manufactured for location in Illinois prior to manufacturing the model unless the provisions for reciprocity are met; each modular dwelling unit shall bear an Illinois seal unless the unit bears a seal from a state which has a reciprocity agreement with this State; the approved inspection agency must place a label of approval on the finished unit before it is shipped from the plant
ilga.gov
815 ILCS 362/10(c): unlike manufactured homes, the local building official may require additional items other than the minimum State requirements to be incorporated into the construction of a modular housing unit
ilga.gov
625 ILCS 5/1-128, house trailer: a trailer or semitrailer equipped and used for living quarters or for human habitation (temporarily or permanently). 625 ILCS 5/1-210.01, travel trailer: a trailer, not used commercially, designed to provide living quarters for recreational, camping or travel use, and of a size or weight not requiring an overdimension permit when towed on a highway
ilga.gov
Illinois Department of Public Health, Regulation of Factory Built Structures in Illinois (2007): the construction of all factory built housing located in Illinois must be approved by either the U.S. Department of Housing and Urban Development or the Illinois Department of Public Health; neither the state nor the federal government regulates the construction of recreational vehicles
idph.illinois.gov
City of Chicago, Additional Dwelling Units Ordinance, home, eligibility and requirements pages: first approved by City Council in 2020 with five pilot areas, expanded by a Council vote in September 2025; ADUs allowed by right in all multi-unit residential and certain business and commercial zoning districts; RS1, RS2 and RS3 properties only within an ADU-Allowed RS Area created by ordinance (Municipal Code 17-7-0754), some with annual block caps and an owner occupancy requirement; a single coach house is allowed and may only be constructed after the principal building; no additional parking is required; no short-term rentals in coach houses constructed after 2021; coach house contractors must participate in Registered Apprenticeship Programs; pre-certification by the Department of Housing, then permits from the Department of Buildings
chicago.gov

04 — Related questions

Where can you put a tiny home in the US?Are tiny homes legal in every US state?What is IRC Appendix Q?Can you put a tiny house in your backyard in the US?Are tiny homes legal in Michigan, and where can you put one?Are tiny homes legal in Kansas, and where can you put one?

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