What is the Cook County 7% Homeowner Improvement Exemption?

The Cook County Assessor's Home Improvement Exemption shields up to $75,000 of new fair-cash value on a residential property for four assessment years after qualifying construction is completed, effectively neutralizing the property-tax bump that would otherwise follow a permitted addition. The legal anchor is 35 ILCS 200/15-180 of the Illinois Property Tax Code, which the Assessor administers under file code HIE.

Qualifying work has to add living square footage or substantially rehabilitate existing space — additions, dormer pop-ups, finished attics, attached garages, deck conversions to three-season rooms, and gut-rehab interior work all qualify. Like-for-like maintenance does not: re-roofing, vinyl-siding replacement, window swaps with the same opening, kitchen and bath cosmetic refreshes, and HVAC equipment changes are explicitly excluded. The dollar cap is on the increase in market value, not the cost of construction, so a $40,000 attic build-out that the Assessor values at $30,000 of new value uses only $30,000 of the $75,000 ceiling.

Filing rules are unforgiving. The application must be submitted within three years of the year the improvement was completed, and 'completed' is interpreted as the date the City of Chicago closed the building permit (final inspection signed off in DOB Permits & Inspections). Retroactive claims beyond that 36-month window are denied — there is no statutory waiver. File online through the Cook County Assessor's Smart File portal; you upload the closed permit, photos of finished work, and a sworn affidavit that the property remains owner-occupied. The Assessor cross-references CDOB permit data and may request a field inspection.

The exemption rides with the property, not the owner, so a sale during the four-year window transfers the remaining benefit to the buyer if it was already on file. After year four, the new value rolls into the assessment base in full, which is why owners often time a kitchen refresh or roof replacement to overlap with year three of a prior addition's exemption — concurrent work does not extend the clock.