From tax year 2023 through 2025, the Cook County Board of Review cut 4,687 commercial and industrial PIN-level assessments under decrease code 3, which covers vacancy along with demolition, fire, natural disaster, exempt status and Certificates of Error. The median cut on those decisions was 28.8% of the Assessor's value. Across all 54,204 commercial and industrial decreases in those years, it was 17.5%.
At the Assessor, the limits show just as clearly. In the same three years, 977 commercial (class 5) appeals got a change citing the property's total vacancy. 1,353 got no change with a reason saying the property had used up the years of vacancy relief the Assessor's policy allows. Another 144 no-changes cited a missing vacancy affidavit or missing documentation.
Vacancy relief in Cook is a matter of office policy. The Assessor's Rule 20 says Illinois law has no specific basis for it, and its Vacancy Policy caps relief at 24 months per event. The Board works from its Rules 20 and 21. Here is what each office requires, the partial-year arithmetic, and why files fail.
Quick Answer
Prove vacancy with a month-by-month Vacancy/Occupancy Affidavit, dated interior photographs, an affidavit of the vacancy's duration and reason with listings and ads attached, a 12-month rent roll, utility bills and three years of income documents. The Assessor adjusts the building, never the land, credits half of weighted market or renovation vacancy less the vacancy already in its valuation, and stops after 24 months per event. The Board's Rules 20 and 21 require the same core file. Space with rent payable counts as occupied. Evidence is due by the Assessor's township close and the Board's evidence date.
The two offices side by side
| Assessor | Board of Review | |
|---|---|---|
| Source | Vacancy Policy (dated March 25, 2026), Rule 20 | Rules 20 and 21 |
| Types recognized | Market, renovation, casualty | "Vacancy" grounds |
| What is adjusted | Building only; land is not adjusted for vacancy | Decided on the file; no published formula |
| Formula | Market or renovation: half of weighted annual vacancy, minus the vacancy in the initial valuation. Casualty: weighted vacancy minus the initial vacancy, capped at 90% | Not published |
| Time limit | 24 months of full or partial relief per event | None stated in the rules |
| Affidavit | Vacancy/Occupancy Affidavit, monthly for the last 12 months (separate form for 10 or more stories) | Vacancy/Occupancy Affidavit (BOR G-8), monthly for the year |
| Photos | Interior and exterior, dated or with an attestation (Rule 12) | Dated photographs of the interior vacant space (Rule 21b) |
| Leasing proof | Proof of marketing for rent or sale, such as a listing agreement | Affidavit of duration, reason and leasing attempts, with ads and listings, or why none (Rule 21c) |
| Income documents | Rule 16: income and expense data in SmartFile, IRS schedules for 3 years before the lien date, leases or summaries, related-party affidavit | Rule 20: Schedule E for 3 years before the lien date, prior-year 1040 or latest income statement, leases or rent rolls, related-party affidavit |
| Utility records | Bills for the vacancy period; an affidavit if some months are missing | Not named in Rules 20 and 21 |
| Deadline | Appeal and all evidence by the township close (Rule 10) | Evidence by the Board's date after the close (Rule 14); late evidence only on the Board's request (Rule 13) |
Details the table doesn't show
- Occupied includes rent payable. At both offices, space counts as occupied if rent is being paid or is payable, even when it sits empty.
- No leasing effort needs a reason. Both offices ask why. The Assessor's Rule 20 gives examples: a sale listing, rehabilitation or an eviction case.
- Affidavits need personal knowledge (Assessor Rule 12; Board Rule 17). For an entity, a qualified representative may sign based on inquiry of the people who know the facts.
- Gaps in utility records can be covered by an affidavit at the Assessor. Combined or unfiled returns need an affidavit and a property-level income statement under Board Rule 20.
- Renovation and casualty files need more. Renovation: contractor's statement of work, timeline, permits and the general contractor's contact. Casualty: the fire, flood or disaster report, and insurance claim papers if available.
- The Assessor rarely inspects to verify occupancy, so the file has to carry the proof. It also checks whether the current value already reflects a prior vacancy revision before granting more.
Timing against January 1 and the windows
The lien date anchors everything. January 1 of the tax year sets the three-year lookback for income documents and the Assessor's one-year photo window. The Assessor's affidavit covers the last 12 months; the Board's form records a stated year. Make the two filings tell the same story.
The Assessor's window is short and hard. Owners typically have 30 days after the reassessment notice, and under Rule 10 the appeal and all evidence are due by the township close.
The Board adds an evidence date. Each township is open at least 30 days. In the Board's 2026 session schedule, evidence for the first groups was due 10 days after each close. Re-review requests are due within 3 days of the decision letter and can't raise new arguments (Rule 26).
Partial-year vacancy, worked
Weighted annual vacancy is the share of space vacant, averaged across the 12 months. That is what the affidavit's monthly rows add up to.
Example. A 100,000-square-foot building has 40,000 square feet vacant from January through June. A new lease fills 30,000 in July, leaving 10,000 vacant through December.
- Weighted annual vacancy: (40,000 × 6 + 10,000 × 6) ÷ (100,000 × 12) = 25%.
- Assessor, market-related: half of 25% is 12.5%. If the initial valuation used 10% vacancy, the building's assessed value comes down 2.5%.
- On a building assessed at $1,000,000, that is $25,000 of assessed value. At the tax year 2024 state equalizer of 3.0355, it is $75,888 of equalized value. At 7.479%, the median tax rate on Cook commercial parcels in tax year 2024, it is about $5,676 of tax.
The Assessor's own example uses 60% weighted vacancy: half is 30%, less 10%, for a 20% cut, or about $45,405 of tax on the same building. Casualty vacancy is not halved: 60% less 10% is a 50% cut, capped at 90%.
The break-even point. For market or renovation vacancy, nothing comes off at the Assessor unless weighted vacancy is more than twice the vacancy in the initial valuation. Find that figure in the income approach behind the assessment, through the Assessor's township valuation reports.
The Board publishes no formula. It decides each file on its evidence.
Why vacancy claims fail
- The time limit ran out. 1,353 commercial no-changes at the Assessor in 2023 through 2025 cited the policy's limit on years of vacancy relief, more than the 977 changes granted for total vacancy.
- The affidavit or documents were missing. 144 commercial no-changes at the Assessor cited exactly that. At the Board, missing documentation has its own no-change code; see the paperwork losses on attorney-filed appeals.
- The vacancy was already in the model, or a prior vacancy revision was still in the value.
- Rent was still payable, so the space counted as occupied.
- The vacancy was within the owner's control. The Assessor requires conditions outside the owner's control, and for market vacancy an occupant-ready building and good-faith leasing.
- Proof was thin: no marketing evidence or explanation, undated or exterior-only photos, or missing income documents.
- Evidence came in late, or a field check was requested in place of evidence.
Where Censum fits
Censum Docket gives a firm a research read on any Cook PIN: argument, comps, recent-sale signal, exemption lane, appeal history and the parcel map. Its deadline cockpit and opportunity queue track live Board of Review windows. A commercial evidence module is offered by separate arrangement. For the income side of the file, see building the commercial income packet.
Censum is not a law firm, does not file appeals and never takes a share of legal fees. The attorney files and makes every legal judgment.
The numbers behind this article
- Board decisions: Censum's tabulation of the Board of Review Appeal Decision History dataset, tax years 2023 through 2025, PIN-level decisions in the "Commercial and Industrial" major class (incentive classes excluded). Code 3 decreases: 1,760 in 2023, 1,716 in 2024 and 1,211 in 2025. Cuts are measured in assessed value against the Assessor's total.
- Assessor appeals: Censum's tabulation of the Assessor's Appeals dataset, tax years 2023 through 2025, class 5 PINs, counting a reason code in any of its three reason fields: code 7 (total vacancy), code 75 (years of vacancy relief exceeded) and code 33 (no vacancy affidavit or documentation).
- Equalizer and rate: PTAXSIM, the Cook County Assessor's Office research database, tax year 2024: final equalizer 3.0355 and median tax code rate across class 5 parcels 7.479%. The Assessor describes PTAXSIM results as not official. The examples are illustrative.
FAQ
Does the Board apply the Assessor's 24-month limit?
Its rules don't state one. The Board decides each vacancy claim on the file under Rules 20 and 21.
Does vacancy reduce the land value?
Not at the Assessor. Its policy adjusts the building only.
Can a vacancy claim go to the Board after the Assessor denies it?
Yes. The Board says it is not bound by the Assessor's decision, and a denial there puts the owner at no disadvantage.
Does Censum file or represent clients?
No. Censum LLC is independent property-tax intelligence and docket software. It is not a law firm. The attorney files and makes every legal judgment.
Sources
- Cook County Assessor, Vacancy Policy and PDF dated March 25, 2026
- Cook County Assessor, Official Appeal Rules (2026), Rules 10, 12, 16 and 20
- Cook County Assessor, Industrial/Commercial Appeals (forms, including the Vacancy Affidavit and the 10-or-more-stories version)
- Cook County Assessor, Overview of How Appeals Work
- Cook County Board of Review Official Rules, Rules 13, 14, 17, 20, 21 and 26, last updated July 27, 2026
- Cook County Board of Review, Vacancy/Occupancy Affidavit, 2026 (PDF)
- Cook County Board of Review, decision reason codes (BOR Form 195, PDF)
- Cook County Board of Review, 2026 session dates and deadlines (PDF)
- Cook County Board of Review, Frequently Asked Questions
- Censum: Commercial appeals win one time in three; build the income packet
- Censum tabulation of the Board of Review Appeal Decision History dataset and the Assessor Appeals dataset (Cook County open data), tax years 2023-2025.
- Censum tabulation of PTAXSIM (Cook County Assessor's Office), tax year 2024.
Sources accessed November 11, 2026.
Next step
Check each vacancy file against both offices' lists before the next township opens, and start with a first read on the PIN in Docket. See Censum Docket
Censum LLC is a data and analytics company, not a law firm and not a tax advisor. Censum is independent and is not affiliated with Cook County or any government agency.