How Properties are Valued

The Cook County's Assessor's Office is responsible for valuing the more than 1.8 million parcels in Cook County. Illinois law requires that the estimated property value and assessed valuation of your property be periodically updated for real estate tax purposes. 

Cook County is divided into three areas, the northern suburbs, southern suburbs, and the City of Chicago. Each of these areas is valued once every three years. Furthermore, Cook County is divided into 36 townships for assessment purposes. 

Residential properties are assessed as of January 1st of the current year, using three to five years of prior sales information. By using multiple sale years, this increases the stability of market value estimates.

The Cook County Assessor's Office uses mass appraisal to produce property values. Instead of appraising property one-by-one, mass appraisal looks to the real estate market to detect local trends in property values based on location and characteristics. Those trends are used to estimate the fair market value of each property based on its location and characteristics. Mass appraisal is a way to put fairness into the assessment system.

Fair Market Value and Assessed Value

Learn how different types of property are valued and how assessments fit into the overall property tax system of Cook County.

Your Assessed Valuation and Property Taxes

The overall amount of real estate taxes to be collected in your community is determined, not by the Assessor nor any single government official, but by all local taxing bodies providing services in your community, such as schools, parks, pensions, and library districts. The assessed valuation of your property does determine your share of those taxes. It is important, therefore, to you and to our office, that your assessed valuation be accurate and fair.

Appealing Your Assessment

Appeals may only be filed during certain periods of time. Please read the general information about appeals for important information about rules for filing and deadlines for your area. You do not need to hire an attorney to file an appeal and filing is free at our office.

The Assessor's Office updates its determination of each property’s fair market value and corresponding assessed value once every three years. A residential property owner might determine the fair market value of their home is accurate. But property owners have a right to challenge the accuracy of those updated values by filing an appeal. If an appeal seeking a lower fair market value is granted, the property’s assessed value is lowered as well.

You do not need an attorney or a tax representative to file an appeal. Personal assistance and information, including forms and specific guidelines for filing appeals, are available from our Taxpayer Services Department. In the suburbs, assistance is also available from the local township assessor.

If you do wish to file an appeal with the Assessor's Office, you must do so by the date noted on your reassessment notice. After the Assessor's filing period for appeals has passed, you will have an additional opportunity to file an appeal with the Cook County Board of Review.