Five things actually move an Illinois property tax bill, and they are not equally useful. In rough order of what they are worth to a typical Cook County owner:
1. Claim every exemption you are entitled to
An exemption reduces the taxable value of your home directly, and it is the cheapest saving available because it is not an argument — you either qualify or you do not. The Homeowner, Senior Citizen Homestead, Senior Freeze, Persons with Disabilities, Veterans and Long-Time Occupant exemptions each have their own test. Check which ones apply.
2. Appeal the assessment
An appeal argues that the county's opinion of your property's value is too high compared with similar properties. It is a separate lever from exemptions and the two do not compete: an exemption lowers the taxable value, an appeal lowers the assessment the exemption is applied to, and you can do both in the same year. Appeals are only accepted while your township's window is open — the deadlines page shows when that is.
3. Correct what the county has on record
The county's description of your property drives its value. Wrong square footage, a garage or bathroom that does not exist, the wrong class, a building that was demolished — each inflates the assessment until someone corrects it. Where the error is factual rather than a matter of opinion, a Certificate of Error can reach back beyond the current year.
4. Know where you are in the three-year cycle
Cook County reassesses one third of the county each year. A reassessment year is when your value moves most, and it is the year an appeal has the most to work with — but you can appeal in any of the three.
5. Read the comparable assessments yourself
Every assessment is an opinion about how your property compares with others. If similar homes nearby carry lower assessments, that gap is the case. This is the part most people cannot do from their own records, and it is the part an appeal turns on.
Start with your property and the deadlines that apply to it.