2025 Cook County Tentative Multiplier or Equalization Factor Set

The Illinois Department of Revenue announced a tentative 2025 Cook County Equalization Factor of 2.8683 on Tuesday, April 28, 2026.  This tentative 2025 Cook County Equalization Factor is 5.51% lower than the final 2024 Cook County Equalization Factor of 3.0355.  Every year, the Illinois Department of Revenue is legally required to calculate the equalization factor to achieve uniform property assessments throughout the state.  The final 2025 Cook County Equalization Factor will issue in late spring or early summer of 2026 after the 2025 Cook County Board of Review closes all appeals for all 38 Cook County townships and the Cook County Clerk analyzes each local township’s annual budgets.  Historically, the final Cook County Equalization Factor is higher than the announced tentative multiplier.

The Cook County Classification Ordinance requires that the Cook County value property based on use with residential properties which includes single family home and apartment buildings assessed at 10.00% of its market value and commercial and industrial properties assessed at 25.00% of its market value.  By contrast, the average three-year level of assessment is 9.25% for Class 2 (residential) properties, 8.24% for Class 3 (apartment) properties, 24.26% for Class 5A (commercial) properties and 24.89% for Class 5B (industrial) properties.  The three-year average level of assessments (weighted by class) for Cook County property is 11.62%.  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 11.62% to calculate the final equalization factor of 2.88683.

If the median level of assessment for all property in the county varies from the 33 1/3 percent level of assessment required by law, an equalization factor is assigned to bring assessment to the legally mandated level by the Illinois Property Tax Code.