What does the 10% residential assessment level in Cook County mean for my home's value?

Cook County does not tax your home on its full market value directly. Instead, under the county's classification ordinance, Class 2 residential property is assessed at 10% of its estimated fair market value. Class 2 covers single-family homes, condominiums, co-ops, and small apartment buildings of six units or fewer. See the Assessor's Your Assessment Notice and Tax Bill and Classifications of Real Property.

The math. Assessed Value = 10% × Fair Market Value. So if the Assessor lists your assessed value as $40,000, the office is asserting your home's fair market value is about $400,000. To check whether you are over-assessed, multiply your assessed value by 10 and ask whether your home would realistically sell for that amount.

Why this matters on appeal. Because the 10% level is fixed by ordinance and applies to all Class 2 homes equally, you cannot win an appeal by arguing the ratio is wrong. You win by showing the fair market value is too high (your home would not sell for the implied amount) or that your home is assessed unequally — taxed at a higher effective level than comparable nearby homes. Both arguments work backward from the assessed value through the 10% level.

One more step to your tax bill. The assessed value is not the final taxable figure. Illinois applies a state equalization factor (the "multiplier") to produce the Equalized Assessed Value, then subtracts exemptions, before the local tax rate is applied. The 10% assessed value is the number you contest in an assessment appeal; the equalizer and rate are set elsewhere. Confirm your property's current assessed value and classification by PIN on the Assessor's site.