Key Word Definitions


The elected official responsible for establishing the assessed valuation for all parcels of real estate in the County and notifying taxpayers of its proposed change of the valuation. Complaints are filed at the Assessor’ office contesting assessed valuations, unlike in the collar counties where no complaint is filed before the Assessor.

Assessed Valuation / Assessment Factors

The total valuation promulgated by the Assessor which includes an assessment for the land (the total site area) and the improvements located upon the site. In Cook County the following assessment factors are applied to the Assessor’s determination of market value to determine the assessed valuation:

10% 25%
Vacant Land, Multi-Unit Apartments, Single Family Homes, Residential Condos and Co-Ops, Mixed Use with less than 7 apartment units, Commercial & Industrial with tax incentive Commercial, Industrial Buildings, and Commercial Condominiums

Properties of all types are assessed in each other county of the state at 33 1/3% of market value.

Board of Review

An administrative body headed by three elected Commissioners, elected in Cook County, appointed in other counties, which, pursuant to a timely filed complaint, reviews/revises assessments promulgated by the Assessor.

Certificate of Error

A procedure allowing a taxpayer to apply for a partial refund of a paid tax bill based upon the over assessment of the property due to certain unusual circumstances. This procedure is generally available for only 1-3 prior years taxes and requires various administrative and/or judicial approvals.

Illinois Property Tax Appeal Board (PTAB)

The state administrative body composed of five members appointed by the Governor which, pursuant to a timely filed complaint, reviews/revises assessments as determined by County Boards of Review throughout the state. The filing of a Board of Review complaint contesting the assessment is a prerequisite to filing a complaint before the Illinois Property Tax Appeal Board. If successful, a portion of the tax will be refunded.

Local Tax Rate

The taxing districts (municipality, schools, park districts, police and fire departments, etc.) within each county submit their budgetary requests to the County Clerk each year. These districts are all enumerated on the second installment tax bill in Cook County. When the assessments for the entire County are finalized by the Assessor and Board of Review, and the State Equalizer has been formulated, a tax rate to meet those budgetary requests is promulgated. (See Chicago Tax Rates & Cook County Equalization Factors)

State Equalizer

Each year the Illinois Department of Revenue reviews the total assessed valuation of each county and examines assessments made by the local assessors to determine whether or not the assessments are based on an accurate analysis of real estate values within the county. If it is determined that the assessments are lower than values would indicate an “equalization” factor is developed by the Department of Revenue which is then made applicable to all property within Cook County.

Tax Rate Objection

A complaint filed in the Circuit Court of Cook County contesting the imposition/amount of a local tax levy. The conditions for filing the complaint are that the tax must have been paid on time and in full.

Tax Objection Complaint (Specific Objection)

An alternate remedy in Cook County to a complaint before the Illinois Property Tax Appeal Board. A complaint is filed in the Circuit Court contesting the final assessed valuation as determined by the Board of Review. The action is defended by the County State’s Attorney’s Office. Conditions for filing the complaint are that the tax was timely paid in full and that a complaint was filed contesting the assessment before the Board of Review.

Triennial Assessment Period

Cook County has a three-year, triennial period, other counties may have different periods, during which an assessment should remain in effect, barring new improvements, vacancy factors or other material change to property. At the time of inception of a particular reassessment period, the Assessor will reassess the values of each property, and in Cook, a scheduled portion (1/3rd) of the County is reassessed each year (See Cook County Township Map).