Cook County Property Taxes and Your Commercial Lease

Under a net lease, you commonly pay your proportionate share of a building's real estate taxes, on top of rent. Under a gross or modified gross lease, you may pay only your share of increases over a base year or expense stop. Either way, what happens to the building's property tax bill can come back to you. That makes it worth understanding how Cook County's system works before you sign, even though the owner is the party who gets the bill.

Cook County's property tax process has several stages, handled by different offices. The Assessor sets the value, the Board of Review hears appeals, the Illinois Department of Revenue calculates an equalization factor, taxing districts set their levies, the County Clerk calculates rates, and the Treasurer issues and collects bills. Because of this, no single office decides your building's bill. The Assessor says plainly that the assessed value is only one factor.

The Assessor's Office states that Cook County follows a triennial reassessment cycle, with the year depending on the property's township. According to its calendar, the south and west suburbs are being reassessed in 2026, while the north suburbs and the City of Chicago are not, apart from special circumstances. An Assessor's release described 2024 as the next reassessment for properties in Chicago at that time, so on a three-year cycle Chicago's next one would be expected in 2027. Confirm this on the Assessor's calendar.

For most commercial property owners, the Assessor says the assessed value is 25% of fair market value, a level set by Cook County ordinance. To value commercial property, it says, it looks mainly at the potential income the property generates, followed by sales of similar properties, using income and expense data along with vacancy rates and capitalization rates for comparable properties. A change in market assumptions can therefore move a building's value even if nothing about the building has changed.

Values can also move outside the three-year rhythm. The Assessor has described using its authority to revise commercial assessments between reassessments, including one instance of resetting values on a group of large commercial properties. Don't assume an off-cycle year means a flat tax line.

Owners can appeal to the Assessor's Office and then to the Board of Review, and each township has deadlines. The Board of Review says that after an appeal there, a further appeal may go to the Property Tax Appeal Board or the Cook County Circuit Court. The Assessor says appeals to its office are free and that owners need not hire a lawyer, while the Board of Review's rules say corporations, LLCs and other entities must be represented by an attorney there.

The official pages we reviewed do not say that a tenant may file its own appeal. They speak of taxpayers and owners. In a multi-tenant building, the owner usually controls the process in practice, and any tenant rights to require or join an appeal come from the lease and applicable law. Ask your attorney if this matters for your deal, particularly in a single-tenant building where you are effectively paying the whole bill.

Evidence can also involve you. The Assessor's commercial brochure lists rent rolls and leases among common evidence, along with income and expense information, and Board of Review rules require income information for leased property. Your landlord may therefore use your lease in an appeal, so check how the confidentiality clause treats this.

Timing in Cook County can trip up a lease. Illinois's Department of Revenue explains that under accelerated billing, used by Cook County, the first installment is 55% of the previous year's bill. The second installment covers the remainder of the amount due. Bills for one tax year are paid in the following calendar year: in 2026, for example, Cook County announced second installment bills for Tax Year 2025, with a due date of October 1, 2026, after a technology-related delay.

Two consequences follow. First, your lease should say whether you owe taxes assessed for a calendar year or taxes payable in that year, because this affects what you owe at the start and end of the term. Second, final numbers can arrive late, and reconciliations and refunds can follow long after the year in question. A tenant that has moved out can still receive a bill, or be owed money, for years it occupied the space.

Ask your attorney to confirm the lease covers taxes for the years you actually occupied the space, with a clear rule for the first and last partial years and for amounts billed after you leave.

Taxes are rarely capped, and landlords resist doing so, since they do not control the bill. You can still improve your position on how the tax line works.

• ✓Is our share based on a clear fraction, and does the denominator include the whole building?
• ✓If the rent is on a base year, is the base year a fully assessed year, and does it use a value that is not under appeal or temporarily reduced?
• ✓If the landlord's appeal lowers a base-year bill later, does that also reduce our base, and how is that treated?
• ✓Do refunds from appeals flow back to us, net of reasonable costs, including after our lease ends?
• ✓Are penalties for the landlord's late payment excluded, along with taxes on income, transfers and special assessments for other tenants' benefit?
• ✓Is there any protection for an increase caused by a sale, and how does it work?
• ✓Can we see the actual tax bill and the appeal history, and does our audit right cover taxes?
• ✓Do we have a right to ask the landlord to file an appeal, or to file one ourselves if the law allows it?
• ✓If a vacancy reduction applies in one year, does the gross-up treat us fairly in later years?

1. Ask for the last few years of actual tax bills and a current estimate, by parcel number.
2. Check the township and its next reassessment year on the Assessor's calendar.
3. Ask about pending appeals, recent sale activity and any recently expired incentive.
4. Run your budget with a tax increase scenario, labeled as your own assumption and not as a forecast.
5. Have your attorney read the tax, base-year and audit clauses together.

We compare the tax line across every proposal as part of our work for Chicago tenants, because a low tax estimate can make one building look cheaper than it will prove to be. We are not tax advisors, so bring in a property tax attorney or your CPA for a specific question or appeal.