How Cook County and Chicago property tax works

How is the bill calculated?

The Clerk’s 2025 report gives the formula for a sample residential bill: market value as set by the Assessor, times the 10% assessment level, times the equalization factor, minus the homeowner exemption, times the tax rate. Four steps:

1. The Cook County Assessor sets a market value and an assessed value (10% of it for homes).
2. The Illinois Department of Revenue issues the equalization factor so assessments across counties are comparable. The Clerk’s table shows 3.0355 for 2024 and 3.0300 for 2025.
3. Exemptions reduce the equalized assessed value (EAV).
4. The Clerk calculates each taxing district’s rate from its levy and the value inside it, and the total rate is the sum of the districts that cover your parcel.

The Clerk’s office notes that state limits, such as tax caps, can restrict the revenue a district extends. The Assessor reassesses one third of the county each year. The City of Chicago was reassessed for tax year 2024 and will be reassessed again for tax year 2027, payable in 2028 (Cook County Clerk).

What are the rates in Chicago?

The Clerk reports Chicago’s average tax rate, which includes the county, the forest preserve, the city, the school board, the City Colleges, the Park District and the water reclamation district, at 6.619% for 2024 and 6.853% for 2025, a 3.54% rise. Total tax billed in Cook County rose 3.8%, from $19.2 billion to about $19.9 billion. The rate for your parcel depends on its tax code, so use the figure on your bill.

Which exemptions apply?

For the general exemption, Illinois lists $10,000 in counties of 3,000,000 or more people (Cook), $8,000 in contiguous counties and $6,000 elsewhere. The Senior Freeze has other conditions, including the age, ownership, residence and application requirements in § 15-172. The Assessor decides who gets an exemption; confirm on your bill that yours appears.

Example: the median-value home in Chicago

The ACS 2024 gives $341,200 as the median value of owner-occupied homes in Chicago. Using that as a market value, with the 2025 factor and Chicago’s 2025 average rate, which is not the rate of any one parcel:

Without the exemption the bill would be $7,084.88, so the $10,000 exemption saves $685.30. A senior who also gets the $8,000 exemption would save another $548.24 at that rate. For comparison, the Clerk’s report puts the average 2025 bill for a single-family home in north Chicago at $7,000.87 on an estimated market value of $370,150.

When are bills due?

Cook County mails estimated first-installment bills by January 31, set at 55% of the prior year’s bill. Actual bills follow by June 30 and show the balance (35 ILCS 200/21-30). The Clerk says 2025 second-installment bills are due October 1, 2026. For tax year 2023 and later, late taxes in a county of 3,000,000 or more carry interest of 0.75% per month (§ 21-15).

Because bills are paid after the year they cover, a seller and buyer share the year by contract. See closing costs in Illinois. Lenders often collect through an escrow account.

How do I appeal an assessment?

1. Assessor. The Cook County Assessor sets the value, so start with its notice and its review options.
2. Board of Review. The Cook County Board of Review hears assessment appeals, township by township. Its site says it is accepting appeals now; check your township’s window.
3. Property Tax Appeal Board (PTAB). If the Board of Review decision disappoints you, you can appeal within 30 days of the notice, or 30 days after the Board transmits its final action on your township, whichever is later (35 ILCS 200/16-160).

PTAB reviews assessments only. It cannot review the amount of a tax bill, the rate, or grant an exemption. See the Chicago guide for the city picture.