The Cook County Assessor’s Office plays an important role in the property tax process and keeping taxes fair and accurate across the county. Here are the basics:
Researching the fair market value
Fair market values refer to what a property would have likely sold for in its most recent assessment year. Identifying fair market values means local governments have an accurate sense of how much each property is worth so that taxes can be shared fairly across the region.
To do this, we use a widely accepted process called mass appraisal. This means our team members don’t visit individual homes. Mass appraisal uses data and statistical formulas to accurately assess the property values in a neighborhood.
We start by reviewing two important things:
Your home's characteristics (its basic features)
Sales of similar, comparable homes (commonly called comps) near your property
Property Characteristics
First, we need to learn more about your home. Here are a few examples of characteristics we look at:
Why do we review this information? We use sales of properties similar to yours to determine the value of your home. To do that, we have to know the basics of YOUR property first to identify which ones are similar.
Comparable Property Sales (Comps)
Comps, or comparable property sales, are properties that have similar characteristics in the same area as your property. These comps give us important information that we use to calculate your property’s current value.
What we do with the comp sales information
Here’s how it works:
- Gathering information: Our Computer Assisted Mass Appraisal (CAMA) system takes information about sales of similar, local properties. It then creates estimates of current property values using different mathematical models.
- Testing: We test hundreds of these models, comparing each estimate of a property’s value with the most recent actual sale price.
- Choosing the model: We find the most accurate model. We also make sure the model follows best practices for fair assessments.
- Estimating the properties in the region: We then use the best model to estimate the values of all homes in an area.
- Reviewing what we find and making corrections: Our staff analysts review these estimates for every neighborhood, correcting any issues.
Sharing the updated value with you
Every year, we reassess properties in either Chicago, the northern suburbs, or the western suburbs. If it is the year for your property to be assessed, you will get a reassessment letter and notice in the mail sharing your new updated assessed property value.
We also share the information on our website in the valuation reports. Each report shows home sale trends and assessment changes for every neighborhood, organized by township.
Filing an appeal
If you think there is an issue with your new updated home value, you will have an opportunity to appeal and ask the Assessor’s Office to review your information. You can look for the deadline on the bottom of your reassessment notice or get on our newsletter list to get updates. (share reassessment notice image?)
Some common reasons for appeals include:
- Not realizing you were eligible for an exemption, a type of property tax savings that property owners may be entitled to
You can also file an appeal through another government agency called the Board of Review.
You do not need a lawyer to file an appeal.
Finalizing your home’s value
Once your home’s value is finalized, the information is shared with the Cook County Treasurer’s Office. They take 10% of your home’s value after any exemptions to determine the Assessed Value. This information is used to determine how much you will owe in upcoming property taxes.
- What’s a township?
Township refers to areas that are grouped together for purposes related to the Assessor’s Office.
In suburban Cook County, this means X.
In Chicago, this means X.
- How other information do you share about your process?
We publish a self-evaluation about the quality of our assessments, based on measurements from the International Association of Assessing Officers. These self-evaluations and valuation reports:
Allow community members to see the accuracy of our work
- Provide property owners with data they can use to evaluate the accuracy of the assessments of their homes and neighborhoods
- How can I see more data about this process?
We released a more detailed explanation of how this works here. We also released all the code for our residential models publicly on GitHub, a platform that hosts open source data. You can view our modeling pipelines for single-family homes, and for condos. You can also review our models and the results of our model on the Cook County Open Data Portal here.