David Orr, Cook County Clerk
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Tax Extension

The Clerk's Tax Extension Unit is responsible for calculating property tax rates for all local governments, or taxing districts, in Cook County that authorize the collection of revenue through real estate taxes.

How tax rates are calculated:

  • The Cook County Assessor's office establishes property valuations.
  • Taxing districts file their levy requests with the Clerk's Tax Extension Unit.
  • To produce the revenue requested, the Tax Extension Unit uses the levy to determine the tax amount to be "extended" against all properties located within the boundaries of the taxing district.
  • The Clerk's Tax Extension Unit determines the rate needed per $100 of taxable value to generate the requested revenue, based on the value of all taxable property within the district boundaries.

(Note: Limits under Illinois law can restrict the revenue, either through statutory maximum rates for certain purposes and/or through "tax caps," which limit the total amount extended. Extension limits are not applied to funds needed to pay bonds and certain other charges.) 


Tax data available online:

Filing deadlines for taxing districts

  • Budgets and Appropriation Ordinance
    Must be filed within 30 days of their adoption. Included with the filing must be an estimate of revenue, by source, for the following fiscal year signed by the chief financial officer of the district.

  • Tax Levies
    Must be filed on or before the last Tuesday in December of the given tax year.

  • Truth in Taxation
    A certificate stating compliance with the Truth in Taxation Law must be filed with the levy ordinance. You may download a sample copy of a Truth in Taxation Certificate*.

  • Annual Financial, Treasurer and Audit Reports
    Many taxing districts must file these reports within six months from the end of the fiscal year.

For more information

Please see the applicable provisions of the Illinois Compiled Statutes. Filing requirements for different types of taxing districts vary, and many requirements change periodically.

You may also e-mail questions to the Clerk's Tax Extension Unit at tax.extension@cookcountyil.gov.

Need more help?

Go to Tax FAQs