The statutory ceiling
Read this as a penalty per redemption period, not as an annual interest rate. Bidders compete by accepting a lower penalty, so what you earn is set at the auction. There is no statutory minimum return.
No minimum rate
Illinois sets no statutory minimum return. Because the rate is not bid down, competition shows up in the penalty rate instead, which is what erodes your yield.
How interest accrues
The penalty does not accrue daily or monthly. Section 21-355(b) charges the certificate amount times the penalty bid if redemption happens within 6 months of the sale, times 2 in months 6 to 12, times 3 in months 12 to 18, times 4 in months 18 to 24, times 5 in months 24 to 30, and times 6 in months 30 to 36. A redemption one day into a new step pays the whole step. Subsequent taxes the certificate holder posts carry a separate 12 percent penalty for each year or portion of a year until redemption. Certificates the county holds as trustee in counties with more than 3,000,000 inhabitants accrue at 0.75 percent per month instead of in six-month steps, and a county that buys at the sale under Section 21-190 takes a 0.75 percent per month penalty bid.
How the penalty bidding works
Read the 9 percent figure as a penalty per redemption period, not as an annual interest rate. Section 21-215 caps the bid at 9 percent of the tax or special assessment and sets no floor, so bidding runs down to 0 percent and a 0 percent certificate returns only what was paid. Section 21-355 then charges that penalty once for the first six months after the sale and adds it again for each further six-month step, which is why a 9 percent bid costs the owner about 18 percent over a full year. Investors accept very low penalties on parcels they intend to take to a tax deed. Certificate life: a certificate is void unless the deed is taken out in the time allowed and recorded within one year after the redemption period expires, so the outside life is roughly four years from the sale on the standard track.
When the certificates sell
No single statewide month. In counties with fewer than 3,000,000 inhabitants the collector must apply for judgment and order of sale within 90 days after the second installment due date, and the sale begins on a date within 5 business days after the application date. In Cook County the application is made within 365 days of the second installment due date, and recent Cook sales have been moved by separate statutory deadlines. Check the county collector page for the current cycle.
The headline figure is a ceiling, not a forecast. To see what a certificate actually pays over a real holding period, run the numbers in the yield calculator, and compare Illinois against other states on interest rates by state.
Verified Jul 29, 2026 against Illinois statutes.
Tax Sale Atlas publishes educational information about public tax sale processes. This is not legal, financial, or investment advice. Rules, dates, and fees change; confirm with the county office before you bid.