Quick answerIllinois sells tax lien certificates for unpaid property taxes. Lien buyers can earn Penalty bid down from a statutory maximum of 9% per 6-month period (18% annualized); the winning (lowest) penalty percentage is applied to the certificate amount at sale and again every 6 months thereafter (35 ILCS 200/21-215, as reduced from 18% per 6-month period by P.A. 102-0363; 35 ILCS 200/21-355). Subsequent taxes paid by the buyer earn 12% per year.. Redemption: Generally 2.5 years from the date of sale; 1 year for vacant non-farm property, commercial or industrial property, and property with a structure of 7 or more residential units (certificates issued on or after January 1, 2024, per 35 ILCS 200/21-350 as amended by the 103rd General Assembly). The certificate holder may extend the period, up to a maximum of 3 years (35 ILCS 200/21-385). Sales: Annual tax sale held by each county collector, typically in the fall (roughly October-December; Cook County's annual sale for tax year 2023 was scheduled December 15, 2026). A separate biennial scavenger sale covers parcels delinquent over multiple years in Cook County. Governing law: Illinois Property Tax Code, 35 ILCS 200/21 (esp. 21-215 penalty bids, 21-350 redemption, 21-355 amount of redemption) and 35 ILCS 200/22 (tax deeds).