How Residential Property Is Valued

The Cook County's Assessor's Office is responsible for valuing the more than 1.3 million residential parcels in Cook County. Cook County is divided into three assessment districts (City, North and South). Each of the assessment districts is valued once every three years.

The Cook County Assessor's Office uses a computer-assisted mass appraisal method to value residential properties. This computerized sales comparison model considers several different value components including, but not limited to,  sales of comparable properties, land, location, building square footage, and construction type. These are some of the very same factors that would be considered by an appraiser seeking to value an individual property.

Residential properties are assessed as of January 1st of the current year, using three to five years of prior sales information. By using multiple sale years, this increases the stability of market value predictions.

Uniformity Between Properties

Our appraisal method reviews all the sales within a neighborhood and estimates a market value by assigning values to the individual building characteristics of sold properties. The market values of all properties (sold and unsold) are determined by using the value estimates. Adjustments are made for disparities discovered when comparing the building characteristics, thereby accounting for differences (like age, quality of construction, size, etc.) between properties.Any necessary final adjustments are made to ensure a fair and uniform assessment of all residential properties.

It is important to note that only properties located in the same neighborhood are compared to each other. Neighborhood codes define the geographic area within which home sales will be compared during the reassessment analysis. Neighborhood codes are determined primarily by differences in sale prices, housing stock and/or geographical factors. In order to create a neighborhood code, the listed factors are considered and field inspections are conducted for each township as it is reassessed. Analysts also meet with the township assessors to refine their neighborhood codes.

Innovative Procedures

A “teardown sale” is a property that is bought for the land, with the older (and typically smaller) home on it being demolished for new construction. Analysts will study sales over the last five years to see if they are the result of tear downs.

If a teardown sale is found, it is deleted from the sales comparison model and therefore will not influence the valuation of the larger homes. The new property would be valued using the new building's characteristics and valued according to its new size and class. All home sales that have been purchased for teardown purposes will be excluded from the overall sales pool to ensure uniformity and fairness. However, removing these sales does not necessarily curb the assessment increases that might be seen for the smaller homes. When many smaller homes are being sold in an area, the valuation of these homes is determined primarily by the recent overall median sales trends and prices.

Homeowners are encouraged to review their property's assessment in comparison to similar properties on the office's Web site. Access the “Online Tool” icon, then click onto “Residential Property Search."