What is the Illinois state equalization factor (multiplier), and how does it affect my Cook County tax bill?
What is the Illinois state equalization factor (multiplier), and how does it affect my Cook County tax bill?
The state equalization factor (multiplier) is a number the Illinois Department of Revenue sets each year to bring a county's assessments to a uniform statewide level — for 2024 Cook County's final multiplier was 3.0355, and your Equalized Assessed Value equals your assessed value times that factor.
Illinois requires that property across the state be assessed at a uniform level (one-third of fair market value statewide). Because Cook County assesses residential property at only 10% of market value under its own classification ordinance, the Illinois Department of Revenue applies an equalization factor — the "multiplier" or "equalizer" — to raise Cook County assessments to the statewide standard.
The formula. Equalized Assessed Value (EAV) = Assessed Value × Equalizer. The Assessor explains: "with an Equalizer of 3.0, a home with an assessed value of $50,000 would have an EAV of 3.0 × $50,000 = $150,000." The EAV — not the raw assessed value — is what local exemptions are subtracted from and what the tax rate is applied to. See the Assessor's Your Assessment Notice and Tax Bill.
The current figure. The Illinois Department of Revenue announced a final 2024 Cook County equalization factor of 3.0355 (announced May 29, 2025). The Department sets the multiplier by comparing actual selling prices to assessed values over a three-year period; the three-year median level of assessments for Cook County was about 10.98%. See the Department's 2024 Cook County Final Multiplier announcement.
Why you cannot appeal the multiplier. The equalizer is set county-wide by the state and applies identically to every property, so it is not something an individual homeowner can challenge in an assessment appeal. What you can challenge is your underlying assessed value — the 10%-of-market-value figure the Assessor assigned. Lowering that number flows straight through the multiplier and reduces your EAV and ultimately your tax. Focus your appeal evidence on market value and on unequal treatment relative to comparable homes, not on the equalizer.