2025 Cook County Final Multiplier or Equalization Factor Set
On June 16, 2026, the Illinois Department of Revenue (DOR) announced that the final 2025 Cook County Equalization Factor is 3.0300. This final 2025 Cook County Equalization Factor is almost identical (-.18%) to the 2024 Cook County Equalization Factor of 3.0355. The final 2025 Cook County Equalization Factor is 5.64% higher than the tentative 2025 Cook County Equalization Factor set on April 28, 2026 of 2.8683.
Every year, the DOR is legally required to calculate the equalization factor to achieve uniform property assessments throughout the state. The DOR determines the equalization factor for each county by comparing the three-year period (2022-2024) of the actual selling prices of individual properties to the assessed values placed on those properties by the county assessor. If the median level of assessment for all properties in the county varies from the 33 1/3 percent level of assessment required by law, an equalization factor is assigned to bring the assessment to the legally mandated level by the Illinois Property Tax Code. A 1.00 factor means that the assessments are accurate and in line with the statewide standard. A 3.0300 factor indicates that Cook County’s assessments as a percentage of market value are significantly lower than required, and therefore, a large upward adjustment is needed to equalize them to the state’s mandate of a 33-1/3 percent level of assessment.
Cook County is the only county in Illinois that uses a formal property tax classification system. Under this system, different types of property are assessed at different percentages of their market value. Vacant land (Class 1) is assessed at 10% of the property’s market value; Residential (Class 2) and Apartment buildings (Class 3) are assessed at 10% of the property’s market value; and Commercial and Industrial buildings are assessed at 25% of the property’s market value.
By contrast, in the press release issued by the DOR, the average three-year level of assessment for Class 1 (vacant properties) is 12.53%; for Class 2 (residential) properties9.15%; 7.89% for Class 3 (apartment) properties, 20.79% for Class 5A (commercial) properties and 23.08% for Class 5B (industrial) properties. Cumulatively, the three-year average level of assessments (weighted by class) for Cook County property is 11.00%. The Illinois Department of Revenue calculates the final Cook County Equalization Factor or Multiplier by dividing Cook County’s 33.33% level of assessment into the three-year average of 11.00% to calculate the final equalization factor of 3.0300.
Exactly when the second installment 2025 real estate tax bills will be issued has not been set as of the current date, but Cook County Board President Toni Preckwinkle has publicly stated that the 2025 installment tax bills will not issue before September and therefore, will not be due before October, 2026.
On another note, all properties located in the south and southwest townships in Cook County are being reassessed in 2026. The 2026 triennial assessments for properties located in Stickney Township were issued today with a 2026 Cook County Assessor’s filing deadline on August 12, 2026. Please call our office at 312-372-2500, Ext. 132, if you or a client of yours has an interest in getting their new triennial assessment reviewed.
