Illinois requires landlords to make the following disclosures to tenants:
Utilities. Where tenant pays a portion of a master metered utility, landlord must give tenant a copy in writing either as part of the lease or another written agreement of the formula used by the landlord for allocating the public utility payments among the tenants. (765 Ill. Comp. Stat. § 740/5)
Rent concessions. Any rent concessions must be described in the lease, in letters not less than one-half inch in height consisting of the words "Concession Granted," including a memorandum on the margin or across the face of the lease stating the amount or extent and nature of each such concession. Failure to comply is a misdemeanor. (765 Ill. Comp. Stat. §§ 730/0 to 730/6.)
Radon. Landlords are not required to test for radon, but if the landlord tests and learns that a radon hazard is present in the dwelling unit, landlord must disclose this information to current and prospective tenants. If a tenant notifies a landlord that a radon test indicates the existence of a radon hazard in the rental unit, landlord must disclose that risk to any prospective tenant of that unit, unless a subsequent test by the landlord shows that a radon hazard does not exist. Requirements do not apply if the dwelling unit is on the third or higher story above ground level, or when the landlord has undertaken mitigation work and a subsequent test shows that a radon hazard does not exist. (420 Ill. Comp. Stat. §§ 46/15, 46/25)
Check the Illinois statute (765 Ill. Comp. Stat. §§ 730/3, 740/5; 420 Ill. Comp. Stat. §§ 46/15, 46/25) for details on these disclosures. See the Laws and Legal Research section of Nolo for advice on finding and reading statutes and court decisions.
Also, check your local ordinance for any city or county disclosure requirements. To find yours, check your city or county website (many are listed on State and Local Government on the Net), or contact the office of your mayor, city manager, or county administrator.
Finally, see the Required Landlord Disclosures article for details on federally-required landlord disclosures and other information on disclosures about the rental property.