Cook County property tax explained: assessments, the multiplier and two bills a year

Cook County, home to Chicago, has one of the most complicated property tax systems in the country, and one of the heaviest. Census survey figures for 2020 to 2024 put the typical bill at $6,191 a year on a median home worth $324,500, an effective rate of about 1.91%. That is about double the national figure of 0.94%. Illinois as a whole is second only to New Jersey, at 2.01%.

The bill is high, but much of it can be checked and sometimes lowered. Here is how it is built.

Step 1: market value and the three-year cycle

The Cook County Assessor estimates each home’s market value. The county is split into three regions, the City of Chicago, the north suburbs and the south and west suburbs, and each is reassessed once every three years in rotation. In a reassessment year, your notice can jump sharply. In the other two years, it usually stays about the same.

Step 2: assessed value

Homes in Cook County are assessed at 10% of market value. A home the assessor values at $300,000 has an assessed value of $30,000.

Step 3: the multiplier

Illinois then applies a state equalization factor, often called the multiplier, to bring Cook County’s assessments in line with the rest of the state. It has been about 3 in recent years. Multiply the $30,000 assessed value by about 3 and the equalized assessed value is about $90,000.

Step 4: exemptions

Exemptions come off the equalized value. The main ones:

• Homeowner exemption, for your main home, takes $10,000 off equalized value.
• Senior exemption, for owners 65 and older, takes off a further $8,000.
• Senior Citizens Assessment Freeze, for seniors below an income limit, holds the value at a base year.
• Exemptions for veterans and people with disabilities, with their own amounts.

In the example, the homeowner exemption brings $90,000 down to $80,000.

Step 5: the tax rate

Finally, the combined rate of every taxing body that covers your address is applied. That includes the county, the city or village, schools, parks, libraries, the forest preserve and others, often more than a dozen. Combined rates in Cook County commonly fall between about 6% and 12% of equalized value. At 7.5%, the example home’s bill would be $6,000.

Why there are two bills

Cook County splits the year into two installments. The first, due in early spring, is an estimate equal to 55% of the previous year’s total bill. The second makes up the rest, based on the current year’s assessment, exemptions and rates. Because the second bill depends on every local body finishing its budget, it often arrives late, sometimes well into the next year. A big change in your assessment or rates shows up there.

How to appeal

If the assessor’s market value looks too high, you can appeal in up to three places.

1. Cook County Assessor. File during your township’s open window, usually about 30 days after reassessment notices go out. Common grounds are wrong property details (square footage, bedrooms, age) or recent sales of similar homes for less.
2. Cook County Board of Review. A separate body that hears appeals after the assessor, with its own window. You can file here even if you did not appeal to the assessor.
3. Illinois Property Tax Appeal Board, or circuit court, after the Board of Review.

There is no fee to appeal at the first two levels, and many owners file without a lawyer.

Common questions

Why did my Cook County bill jump? Usually because your region was reassessed, a local body raised its levy, or an exemption dropped off, often after a home sale.

How do I check my exemptions? Search your address on the Cook County Assessor’s or Treasurer’s website. Missing exemptions from past years can sometimes be claimed back for a few past years.

Is the effective rate the same across the county? No. Rates vary widely by town and school district, so two homes of equal value can pay very different amounts.