If you own property in Lemont Township, your window to appeal your 2026 assessment closes on September 29, 2026.
Miss it, and your only remaining option is the Board of Review — a separate process with its own deadlines and evidence rules. The Assessor level is where most successful appeals start, and it's the cheapest, fastest place to fix an over-assessment.
Why this deadline matters
Cook County reassesses property on a triennial cycle. When your township opens, you get one shot at the Assessor level before the books close.
Here's the part most homeowners miss: 56% of appeals filed at the Assessor level result in a reduction. But only about 27% of Cook County homeowners actually file. That gap is why residential taxpayers absorbed roughly $500 million in additional tax burden shifted from commercial properties in recent years — the people who didn't appeal paid for the people who did.
If your neighbor appeals and you don't, your share of the tax levy goes up. It's that simple.
How the Assessor-level appeal works
The Cook County Assessor's Office runs an online appeal portal. You file under your PIN, select an appeal reason, and upload evidence. There's no hearing — it's a paper review.
The three arguments that actually work:
- Lack of uniformity. Comparable properties in your neighborhood are assessed lower per square foot than yours.
- Overvaluation. Recent sales — yours or nearby — show market value below the Assessor's estimate.
- Property description error. The Assessor has your square footage, lot size, bedroom count, or building class wrong.
Illinois uses a 10% assessment ratio for residential property, and Cook County applies a state equalization factor (2.9237 in the most recent year) to convert assessed value into equalized assessed value. Small errors in the underlying assessment get multiplied across every line on your tax bill.
What evidence you actually need
The Assessor's office doesn't want a story. It wants data.
A strong Lemont property tax appeal package typically includes:
- 5 to 7 comparable properties within a half-mile radius, similar in age, size, style, and building class, showing lower assessments per square foot.
- Square footage verification — a measurement from your deed, appraisal, or listing that contradicts the Assessor's record.
- Photos if there are condition issues (deferred maintenance, foundation problems, outdated interiors) that a drive-by wouldn't catch.
- Recent sale documents if you bought the home within the last three years for less than the current assessed market value.
The most common winning argument in suburban townships like Lemont is uniformity. If three houses on your block that are the same vintage and roughly the same size are assessed at $280,000 and yours sits at $340,000, that's a filing you can make in an afternoon.
What it costs to appeal
Filing with the Assessor is free. Building the evidence isn't — unless you do it yourself.
Two common paths:
Property tax attorneys typically charge 33% of your first year's tax savings as a contingency fee. If your appeal saves you $1,800, the attorney keeps $600. If it saves you $4,000, they keep $1,320. Some firms also add flat administrative fees on top.
CheckMyTax charges a $99 flat fee for a complete evidence package — comps, uniformity analysis, and a filing-ready PDF you submit yourself through the Assessor's portal. You keep 100% of the savings. If the analysis shows you don't have a case, we tell you before you pay.
We're not a law firm and we don't file on your behalf. For most single-family homeowners doing a straightforward Assessor-level appeal, that's exactly what's needed. For complex commercial or multi-parcel situations, hire an attorney.
What to do before September 29
Work backwards from September 29:
- First: Pull your PIN and current assessment from the Cook County Assessor's website. Confirm the square footage and property characteristics on file are accurate.
- Next: Identify comparable properties or errors. This is the actual work — most homeowners underestimate how specific the comps have to be.
- Before the deadline: File. Don't wait for the last day. The portal gets slow, and any technical issue that pushes you past midnight on the 29th ends your appeal.
The realistic outcome
Appeal outcomes vary. Even with strong evidence, the Assessor may reduce your assessment partially, fully, or not at all. A denial at the Assessor level doesn't end things — you can refile at the Board of Review when Lemont opens there.
But the median successful residential appeal in Cook County shaves several thousand dollars off assessed value, which typically translates to a few hundred to over a thousand dollars in annual tax savings depending on your local rate. Compound that over the three years until the next reassessment, and the math is straightforward.
The Lemont deadline isn't moving. September 29, 2026. Filing takes an afternoon. Not filing costs you every year until the next reassessment cycle.
Source: Cook County Assessor Assessment Calendar and Deadlines.