- Assessment basis
- Statutory 33⅓% of market outside Cook; Cook County classifies by ordinance — 10% residential vs 25% commercial/industrial levels of assessment — then the state equalization factor (multiplier) applies: NOMINAL RATIOS ≠ EFFECTIVE burden.
- Reassessment cycle
- Cook County: TRIENNIAL reassessment by geographic district (City of Chicago / North / South rotate); rest of IL generally quadrennial with annual adjustments. Assessed at a fraction of market by CLASS under Cook's ordinance — 10% residential, 25% commercial/industrial — then the state multiplier (equalization factor) and local rates apply.
- Reassessment trigger
- Reassessment year for your district; sales, permits, and appeals move values between cycles. No sale-price cap.
- Personal & intangible property
- ILLINOIS TAXES NO BUSINESS PERSONAL PROPERTY (abolished 1979; replaced by the corporate 'personal property replacement tax' on income — not an assessor filing).
- CRE forecasting note
- Cook math: implied market = AV ÷ class level (25% commercial), × state equalizer for taxable EAV. Appeal ladder is unusually deep — Assessor re-review, Board of Review, then PTAB or Circuit Court — and heavily used; classification disputes (class 5 vs incentive classes 6-8) are their own practice area.
- Residential note
- Cook County residential assessed at 10% level (vs 25% commercial); homeowner, senior, and senior-freeze exemptions reduce EAV; triennial reassessment cycle by district; same appeal ladder (Assessor re-review, Board of Review, PTAB).
SPLIT RATE — Cook County classification (10%/25% LOA) + state equalizer.
NO PERSONAL PROPERTY — BPP abolished 1979 — corporate replacement income tax instead.
RATIO CAUTION — 33⅓% statutory level + multipliers: nominal ≠ effective.
Primary sources: Cook County Assessor; IL Dept. of Revenue; Cook classification ordinance (as of 2026-07-01). Confirm current rules and figures with the assessing authority before any use.