35 ILCS 200/14-30
In all counties, all hearings held by the chief county assessment officer in support of or in opposition to a proposed revision or correction in assessed valuation shall be open to the public. All files maintained by the chief county assessment officer relating to the assessed valuation of any property, and all complaints, supporting documents, and other evidence submitted by the complainant shall be available for public inspection during regular office hours of the chief county assessment officer.
If a property owner wishes to support his or her request for a revision or correction of valuation by facts set forth in income tax returns, he or she shall submit the entire return to the chief county assessment officer. However, only the portions of the return relating to the property for which a revision or correction is requested shall be a public record. If requested by the chief county assessment officer, the property owner shall execute a consent in favor of the chief county assessment officer instructing the taxing body with which the income tax return was filed to furnish a certified copy of the return so that the accuracy of the copy submitted to the chief county assessment officer may be verified.
The chief county assessment officer shall promptly furnish to any person copies of all complaints, supporting documents and other evidence submitted by a complainant, subject to the foregoing qualification, and all public records of the chief county assessment officer for a fee of 35 cents per page of legal size or smaller and $1 for each larger page.
35 ILCS 200/14-30