Reviewing property-tax prorations without assuming a statewide formula
Learn to analyze property-tax prorations in Illinois by understanding local tax assessment cycles rather than relying on assumed statewide calculation formulas.
The short answer
Illinois property tax is levied and collected by local government units, not a single state formula. Prorations at closing rely on current assessment cycles, which vary significantly by county. Because Cook County assesses residential property at 10 percent of fair market value while other counties typically use 33 1/3 percent, your specific county assessment level is critical for accurate calculations.
Verify Local Assessment Standards
Do not assume a uniform tax rate or assessment level across Illinois. You must determine if the property is in Cook County or another jurisdiction, as this dictates the assessment level used to determine the base value of the tax bill.
Worksheet: Identify your county. List the 2020 Census town-wide assessment level (10% or 33.3%). Contact your local county assessor to confirm if your property type requires a different adjustment before applying proration percentages.
Review Tax Cycles and Payment Timing
Illinois tax bills are typically paid in the year following the assessment year. A common mistake is using the current year's bill for a proration that actually covers the prior year's tax obligation.
Worksheet: Create a timeline. Mark the assessment year and the year the taxes were billed. If you are selling, ensure the proration credit reflects the exact period the seller occupied the home relative to the specific bill cycle.
Check for Homestead and Other Exemptions
Exemptions such as the General Homestead Exemption or Senior Citizens Homestead Exemption directly impact the total tax liability. If the seller qualified for these, the tax amount on their bill may be lower than what the buyer will pay.
Worksheet: List all exemptions currently applied to the property. Consult a professional: 'If I lose the seller's specific exemptions, how should the proration be adjusted to reflect the non-exempt tax liability I will face?'
Analyze Levies and District Changes
Property taxes are determined by equalized assessed value and local taxing district levies. School districts often receive the largest share, and these levies change based on local referenda.
Worksheet: Review the last two years of tax records. Identify if the 'Taxing District' column shows significant variations in the school district or other local service tax rates.
Checklist
- Confirm your county’s specific assessment level percentage.
- Verify if the tax bill covers the current or prior year.
- List all active exemptions currently applied to the property.
- Identify the primary school district levy.
- Ask a tax professional about the impact of losing the seller's specific exemptions.
Common questions
Can I use the seller's tax bill as an exact estimate for my future payments?
No. Because Illinois tax bills are based on local levies and individual exemptions, your tax burden may change based on your eligibility for exemptions like the Homestead Exemption.
Where can I find official assessment records?
Assessment records are public and open to inspection. You should check the county assessor's official website or office to confirm the current assessment data for your specific property.
Sources
- CFPB — Loan Estimate explainerChecked October 12, 2026
- CFPB — Closing Disclosure explainerChecked October 12, 2026
- Illinois Department of Revenue — Property tax overviewChecked October 12, 2026
- IRS Publication 523 — Selling Your HomeChecked October 12, 2026
This guide is general educational content from SQFT IO, prepared with AI assistance. It is not legal, tax or loan advice. Talk with a licensed attorney, tax professional or lender about your situation. SQFT IO Illinois license 478.027617.