Property tax bills represent one of the largest expenses Chicago homeowners face each year, and 2026 assessments are no exception. Cook County’s property tax system can feel confusing and overwhelming, especially when you receive a notice indicating your assessed value has increased significantly. Understanding how the assessment process works and knowing your rights to appeal can save you thousands of dollars annually.
How Cook County Determines Your Property Tax Assessment
The Cook County Assessor’s Office conducts property reassessments on a three-year cycle, dividing the county into three regions, or triads. Each triad undergoes a full reassessment every three years, with the City of Chicago typically reassessed in different years than the northern and southern suburbs. During a reassessment year, the Assessor examines recent property sales, construction permits, property characteristics, and neighborhood trends to establish fair market values.
Your property’s assessed value is calculated as a percentage of its estimated market value. In Cook County, residential properties are assessed at 10% of their market value, while commercial properties face a 25% assessment rate. This assessed value then gets multiplied by the tax rate, which includes levies from multiple taxing bodies including the city, county, school districts, park districts, and other local government entities.
Why Your Assessment Might Increase in 2026
Several factors contribute to rising property assessments in Chicago and surrounding Cook County areas. The real estate market has experienced significant fluctuations over recent years, with some neighborhoods seeing dramatic appreciation while others remain stable or decline. The Assessor’s Office uses comparable sales data, and if properties similar to yours have sold for higher prices, your assessment will likely increase accordingly.
Additionally, any improvements you made to your property, such as renovations, additions, or finishing a basement, can trigger a higher assessment. Even if you haven’t made changes, the Assessor might have updated information about your property that wasn’t previously recorded in their system. Sometimes assessments increase due to corrected square footage, additional bathrooms, or other features the Assessor’s records didn’t previously reflect.
Understanding Your Assessment Notice and Timeline
Cook County mails assessment notices to property owners in waves throughout the reassessment year. When you receive your notice, it will show your property’s previous assessed value, the new proposed assessed value, and the estimated market value the Assessor believes your property is worth. This notice is your first opportunity to determine whether an appeal makes financial sense.
The appeal deadline is critical and varies depending on when your township’s assessments are published. Generally, you have 30 days from the date your township’s assessments are published to file an appeal with the Cook County Assessor’s Office. Missing this deadline means waiting another year or potentially three years before you can challenge your assessment again. The stakes are high because an inflated assessment affects not just one year’s taxes but continues until the next reassessment cycle unless successfully appealed.
Key Evidence That Supports a Successful Appeal
To successfully appeal your property tax assessment, you need compelling evidence showing your property’s assessed value exceeds its actual market value. The most powerful evidence includes recent sales of comparable properties in your neighborhood that sold for less than your estimated market value. These comparables should be similar in size, age, condition, and location to strengthen your case.
Documentation of property defects, needed repairs, or adverse conditions also supports your appeal. If your property requires a new roof, has foundation issues, outdated systems, or other problems that reduce its value, detailed descriptions and cost estimates help demonstrate why your assessment should be lower. Professional appraisals, while not required, provide strong third-party validation of your property’s true market value.
The Three Levels of Property Tax Appeals
Cook County’s appeal process consists of three distinct stages, each offering another opportunity to challenge your assessment. The first level involves filing an appeal directly with the Cook County Assessor’s Office during the initial 30-day window. Many homeowners successfully reduce their assessments at this stage by submitting comparable sales data and supporting documentation.
If the Assessor denies your appeal or you remain unsatisfied with the reduction, the second level involves appealing to the Cook County Board of Review. This independent body conducts hearings and reviews evidence from both the property owner and the Assessor’s Office. The Board of Review typically hears appeals several months after the Assessor’s decision.
The third and final level is the Illinois Property Tax Appeal Board (PTAB), which handles appeals after the Board of Review issues its decision. PTAB appeals are more formal and often benefit from professional legal representation due to the complexity of presenting evidence and arguing legal points.
When Professional Help Makes Sense
While homeowners can navigate the appeal process independently, many situations warrant professional assistance. If your assessment increases substantially, your property taxes exceed $5,000 annually, or you face complex valuation issues, consulting with Aaron Fox Law can provide significant advantages. Experienced property tax attorneys understand what evidence the Assessor and Board of Review find most persuasive and can present your case strategically.
Professional representation becomes especially valuable at the Board of Review and PTAB levels, where procedural requirements and evidence rules become more stringent. Many property tax attorneys work on a contingency basis, charging fees only if they achieve tax savings, making professional help accessible without upfront costs.
Take Action Before the Deadline
Don’t let appeal deadlines pass while your property remains overassessed. Review your assessment notice carefully, research comparable properties in your area, and gather documentation supporting a lower valuation. Whether you appeal independently or seek professional guidance, taking action protects your financial interests and ensures you’re paying only your fair share of property taxes.