Cook County, Illinois property tax

ACS 5-year median real estate taxes paid (table B25103) divided by ACS 5-year median value of owner-occupied housing units (table B25077), county-wide. This is a ratio of two independently estimated medians — not the median of the ratio, and not a rate any parcel is billed. It reflects the actual mix of overlapping districts, exemptions and assessment caps as experienced by owner-occupants, and it lags: a 5-year sample centres about two and a half years before its end date.

Layer 1 of the county property-tax corpus: a MEASURED baseline from ACS 2020-2024 5-year, not a published rate. No statutory rate, assessment ratio or exemption has been collected for these counties yet, so nothing here should be read as what a particular property would be billed.

The equalization factor is where Illinois hides its assessment level, and it must be modelled as one. The Department equalises each county to 33 1/3% of fair cash value, but 35 ILCS 200/17-25 forbids certifying any factor for a county already between 99% and 101% of target — a statutory dead band that is why 83 of 102 counties receive a literal 1.0000. Cook receives 3.0300 for tax year 2025, roughly 2.8 times the next largest in the state, and that number is not an anomaly but the arithmetic consequence of its ordinance: a blended level near 11% against a 33 1/3% target. Because both classes are scaled by the same factor, equalization restores comparability BETWEEN counties without disturbing the 2.5 ratio WITHIN Cook. Note also the tentative-to-final gap is real — the 2025 tentative was 2.8683 against a final of 3.0300, a 5.6% move — so a tentative must never be cached as a final. Two corrections to the usual account. Cook Class 4 not-for-profit is 20%, not the 25% still circulating from pre-2018 tables. And PTELL binds only NON-HOME-RULE taxing districts, which is a large carve-out: Chicago and many municipalities are home rule and sit outside it entirely, so modelling PTELL as a county-wide cap overstates its reach. PTELL is also not statewide — it applies by law only to Cook and the counties contiguous to it, and elsewhere only where voters have adopted it by referendum, on the order of 39 of 102 counties. Citation hazards on Illinois hosts, none detectable by status code. The official Cook County Code at library.municode.com is CLIENT-RENDERED: it returns HTTP 200 with a body of about six kilobytes containing no ordinance text at all, so a link check cannot tell that the citation is empty. The Department's property tax statistics index is likewise client-rendered, with all 1,575 report links injected by a widget and none in the HTML. Several Department PDFs are scanned images with no text layer AND are rotated in place annually, so a URL pinned for one year silently begins serving another while staying HTTP 200. And ilga.gov returns 403 to a default user agent while serving normally to a browser.