The Treasurer's website states:
Any for-profit and not-for-profit business entities that conduct business in Illinois are required to report unclaimed property on an annual basis. If you believe your firm is not holding unclaimed property, the state requires you to file a negative report.
All banking and financial organizations, insurance companies (other than life insurance corporations) and governmental entities are required to file November 1 of each year. The report should reflect account activity for the one-year period five years prior to June 30 of the report year.
Examinations are scheduled when the Treasurer’s Office suspects a holder failed to report property as required by law. The examinations are conducted in compliance with Sections 23, 24.5 and 11.5 of the Uniform Disposition of Unclaimed Property Act and Section 180.90 of the Unclaimed Property Administrative Rules.