A Cook County tax bill is not a percentage of what your home is worth. It is the end of a four-step calculation, and an appeal changes the first number in it.
The four steps
- Market value. The Assessor estimates what the property would sell for.
- Assessed value. A home (Class 2) is assessed at 10% of that market value. A $300,000 house has an assessed value near $30,000.
- Equalized assessed value. The state multiplies the assessed value by the equalization factor — 3.0300 for the 2025 tax year — to bring counties onto a common footing. Exemptions are then subtracted from this number.
- The bill. Your local tax rate, set by the schools, municipality, county and other districts that serve your address, is applied to what is left.
Worked through
$300,000 market value → $30,000 assessed → about $90,900 equalized. Take off the Homeowner Exemption's $10,000 and roughly $80,900 is taxed. At a 7% local rate that is about $5,660 a year; at 13%, about $10,500. The rate is why two identical homes in different townships pay very different bills — see the 2025 rates by township.
Which number an appeal changes
An appeal argues the assessed value, step two. Lower it and every step after it falls with it. It does not change the rate, which is set by the taxing districts, or the equalizer, which is set by the state. Run your own figures in the property tax calculator, or have a property tax attorney look at the assessment itself.