Your Assessment Went Up. Your Tax Bill Hasn’t—Yet.

A higher property assessment can feel like a bill arriving before breakfast, but the two are not the same thing. An assessment is the value the county uses in the tax formula; the actual bill comes later, after local taxing bodies set levies and rates, exemptions are applied, and county calculations are finished.

That distinction matters across suburban Chicagoland, where assessment notices and appeal calendars can move on a township-by-township schedule. A homeowner in Bartlett may follow a different county process than a friend a few blocks away because Bartlett crosses the Cook-DuPage county line. The same boundary wrinkle affects parts of Schaumburg and Hanover Park, while Elgin spans Cook and Kane counties. Carol Stream and Bloomingdale are in DuPage County, and Streamwood is in Cook County.

What the assessment number actually means

Outside Cook County, Illinois generally assesses property at one-third of fair cash value under 35 ILCS 200/9-145. Cook County uses its own classification system; owner-occupied residential property is generally assessed at 10% of market value. Those percentages look dramatically different, but comparing them directly is misleading because equalization factors and local tax rates enter the calculation later.

The practical question is simpler: Does the assessor’s estimate reasonably match the property as of January 1 of the assessment year, and is it being treated consistently with comparable homes?

An assessment increase does not translate dollar-for-dollar into the same percentage increase on the eventual tax bill. Your share of the local tax base matters. So do exemptions, levy changes, equalization, and changes in other properties’ values. That is why “my assessment rose 12%, so my bill will rise 12%” is tempting arithmetic—but not reliable arithmetic.

The clock matters more than the outrage

If a notice lands in your mailbox, read the appeal instructions before launching into a neighborhood group chat. Appeal windows are short and depend on the county and township publication schedule. The deadline printed by the assessor or board of review is the one that controls; do not assume last year’s date applies.

Before filing, check four things

• Property facts: Verify living area, lot size, age, construction type, basement finish, bathrooms, garage spaces, and other characteristics in the assessor’s record.
• Recent comparable sales: Use nearby homes similar in style, size, condition, and location. A remodeled four-bedroom two-story is usually weak evidence for an untouched three-bedroom ranch, even if they share a subdivision entrance.
• Uniformity: Compare assessments—not merely asking prices—with genuinely similar neighboring properties. Illinois appeals can concern either market value or unequal treatment.
• Exemptions: Confirm that any exemption for which you qualify appears correctly. Common examples include the General Homestead Exemption and, when applicable, senior-related exemptions.

Photos can help document condition issues that a spreadsheet misses: an original kitchen, deferred maintenance, foundation trouble, or damage. An appraisal may help in the right case, but it is not automatically necessary for every residential appeal. Follow the county’s evidence rules and submit documents in the requested format.

Buyers should investigate taxes before they inherit the surprise

For a buyer, the seller’s current bill is history—not a guarantee. A recent sale may become evidence of market value, exemptions can disappear after a transfer, and new construction or major improvements may not yet be fully reflected. Ask which county and township govern the parcel, review the assessor’s property record, and check whether the displayed bill includes exemptions that will not transfer to you.

This is especially important around municipal borders. “Bartlett taxes” is not one universal calculation when a property may sit in Cook or DuPage County. The parcel’s county, township, school districts, park district, library district, and other taxing bodies—not the town name on the listing—drive the bill.

Sellers should fix errors before buyers find them

A visibly incorrect record or a startling assessment jump can become a negotiating issue. Sellers in Carol Stream, Bloomingdale, Elgin, Schaumburg, Streamwood, Bartlett, and Hanover Park should pull the public property card early, confirm exemptions, and keep any successful appeal decision or supporting evidence. You may not be able to predict the buyer’s future bill, but you can explain the current record honestly and avoid scrambling after an inspection contingency is already ticking.

The useful response to an assessment increase is neither panic nor procrastination. Check the facts, calendar the deadline, gather comparable evidence, and use the correct county process. If you are buying or selling and want help understanding which public records deserve a closer look, Garry Real Estate can help you organize the questions—without pretending anyone can promise the next tax bill.

Straight outta the brain of Bob, Garry Real Estate’s in-house lead AI. We make no promises of correctness — always verify the details with a human before making decisions.