Illinois assessment is decentralized to townships (in most of the state) or to one assessor (in Cook County). Cook County operates on a triennial reassessment cycle — North Suburbs, South/West Suburbs, and Chicago each reassessed once every three years. Appeals first go to the Cook County Assessor's office, then to the Cook County Board of Review. Statewide, the second step is the Property Tax Appeal Board (PTAB) within 30 days of the Board of Review's decision. Cook County has rolling appeal windows by township.
Verify before filing. Statutory deadlines change, and many counties operate on their own schedule inside the state framework. Always confirm the current year's window with the assessor or appeal board for the specific jurisdiction before relying on a date.
State-level deadlines plus major sub-jurisdictions where the schedule diverges from the state default. Where a column says "Varies," confirm the date with the local assessor.
| Month | Type | Event | Date | Details |
|---|---|---|---|---|
| January | RP | Lien date |
January 1 | Statewide assessment date. |
| Varies | RP | Cook County Assessor — first-level appeals Cook County |
Rolling (~30 days per township) | Cook County opens appeals township by township throughout the year. Each township has roughly a 30-day window after notices issue. |
| Varies | RP | Cook County Board of Review appeals Cook County |
Rolling — 30 days after BoR opens township | Second-level Cook appeal. Board of Review opens townships sequentially after Assessor closes them. |
| Varies | RP | Non-Cook County: County Board of Review |
30 days from publication of assessment changes | Outside Cook, Boards of Review accept complaints for 30 days following publication of changes by township. Some counties have a fixed annual deadline. |
| Varies | RP | PTAB appeal |
30 days from Board of Review final decision | Statewide: Property Tax Appeal Board (PTAB) petitions due within 30 days of the Board of Review's final decision letter. Alternative: file in circuit court. |
RP = Real Property · BPP = Business Personal Property · Both = Applies to both
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