A Winnebago County property owner should first raise a suspected record or valuation problem with the township assessor and, if still dissatisfied, file a formal complaint with the Winnebago County Board of Review during the 30-day period following assessment publication. The exact 2026 dates, current complaint form, and final procedural rules were not yet posted when this page was reviewed July 15, so an owner should not reuse a 2025 form or assume last year's delivery requirements. FairPath can help manually organize the notice, property facts, owner-selected comparisons, condition records, and questions to verify with the Board. It does not file, represent the owner, or claim current instructions that the county has not published.
Assessment context: Winnebago County's process has several levels. Township assessors maintain and can correct assessments while they still hold the books; the county Supervisor of Assessments publishes notices and supports assessment administration; the county Board of Review hears timely formal complaints. If an owner remains dissatisfied after the Board decision, the Illinois Property Tax Appeal Board is a separate later route. The county explains that 2023 was its general assessment year and that 2026 is an intervening year, when publication and mailed notices may focus on parcels changed by the township assessor. Even so, the owner should monitor the official publication and verify the current PIN, township, property description, assessment, and any equalization effect before deciding whether a formal complaint is appropriate.
Filing process: Begin with the current assessment record and contact the township assessor promptly, while recognizing that informal review does not replace the Board complaint. Monitor the official Board of Review page for the 2026 publication date, closing date, rules, and complaint form. As of July 15, the county still displayed 'not yet available' for the 2026 rules. Once posted, use only the 2026 form and follow its signature, copy, evidence, and delivery requirements exactly. The Board and Supervisor of Assessments are located at 404 Elm Street, Room 301, Rockford, Illinois 61101; confirm the accepted filing route with that office if the website remains incomplete. Keep a complete submission copy and dated proof that the Board received or recognized the complaint before the 30-day window closes.
Evidence to review: The current county Board page links a residential Comparable-Property Grid Sheet and a Sales Locator Tool, signaling that comparisons should be structured rather than submitted as an unexplained address list. For a market-value claim, identify relevant arm's-length sales and compare location, living area, age, style, construction, lot, basement, garage, improvements, and condition. For inequity, compare current assessments of truly similar properties using a consistent metric. Dated photographs, measurements, surveys, permits, repair records, or inspection material can support a physical-data or condition difference when labeled and tied to the claimed correction. Because the final 2026 rules were still unavailable, verify the permitted valuation period, number of comparables, copy requirements, and evidence deadline against the posted 2026 form before relying on prior-year practice.
Current deadline guidance: Exact 2026 dates not yet posted; complaints are due 30 calendar days after publication. Winnebago County states that a formal Board of Review complaint is due 30 calendar days after assessments are published. The county says assessments are generally published near the end of July and recommends checking the Board page in mid-July for exact dates. When reviewed July 15, 2026, the page still marked the 2026 Rules and Procedures as not yet available and did not display a final 2026 complaint date. Do not infer a closing date from a prior year. Recheck the official Board page, current assessment publication, and notice before filing.
Winnebago's official 2026 posture was still pending on July 15. The Board page said assessments are generally published near the end of July, advised visitors to check in mid-July, and still labeled the 2026 rules unavailable. This uncertainty should be shown directly rather than converted into an estimated filing date.
The county describes 2023 as the general assessment year, with every fourth year following that cycle. In intervening years such as 2026, publication and notices may apply to parcels changed by the township assessor. Owners should review the current property record and publication instead of assuming every parcel receives the same notice treatment.
The county provides separate residential and commercial or industrial comparable-grid links plus a Sales Locator Tool. A homeowner should use the residential grid applicable to the current 2026 rules, verify all source facts, and explain why each selected property is comparable. Tool output alone is not an argument.
Do not silently carry forward the prior year's paper-copy count or supplemental-evidence period. Earlier Winnebago forms may be useful for understanding the type of information the Board has requested, but the missing 2026 rules mean the current form and direct Board confirmation control filing mechanics.
Official filing authority: Winnebago County Board of Review. https://wincoil.gov/departments/supervisor-of-assessments/board-of-review
Source: Winnebago County Supervisor of Assessments, Board of Review, https://wincoil.gov/departments/supervisor-of-assessments/board-of-review. Reviewed 2026-07-15.
Source: Winnebago County, Supervisor of Assessments, https://wincoil.gov/departments/supervisor-of-assessments/. Reviewed 2026-07-15.
Source: Winnebago County Supervisor of Assessments, Property Assessment Frequently Asked Questions, https://wincoil.gov/departments/supervisor-of-assessments/faqs. Reviewed 2026-07-15.
Source: Illinois Department of Revenue, Property Assessment Appeals, https://tax.illinois.gov/localgovernments/property/appeals.html. Reviewed 2026-07-15.