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Jefferson County · Lake Koshkonong, WILake Koshkonong, WI property taxes. Off the peak. Check your notice.
In January 2026, the typical home in Lake Koshkonong was worth about $209,000, 45.1% below the August 2021 peak of $380,000. If your assessment still reflects peak-era prices, an appeal may be worth filing.
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What Lake Koshkonong home values did
Lake Koshkonong values peaked in August 2021 and were 45.1% lower by January 2026. In the year to January 2026, they fell 13.7%. That's weaker than Jefferson County as a whole (+4.8%).
Values have been roughly flat since January, through August 2026.
| Month | Typical value | vs. a year earlier |
|---|---|---|
| January 2021 | $377,000 | +10.2% |
| January 2022 | $359,000 | -4.7% |
| January 2023 | $273,000 | -23.9% |
| January 2024 | $249,000 | -8.8% |
| January 2025 | $242,000 | -2.8% |
| January 2026 | $209,000 | -13.7% |
| August 2026 (latest) | $208,000 | -0.3% since January |
Peak since 2021: $380,000 in August 2021. January 2026 was 45.1% below it.
What to check on your notice
If your 2026 notice shows a higher value than last year, ask why. The typical Lake Koshkonong home lost 13.7% over the same stretch. A higher number can still be right for a specific home, for example after a remodel, but the municipal assessor should be able to explain it.
How Lake Koshkonong compares nearby
Among 10 Jefferson County places, Lake Koshkonong has the 1st largest drop from its peak and the 10th highest typical value. Statewide, its 1-year change ranks 1st of 681 Wisconsin places, from weakest to strongest.
| Place | January 2026 | 1-year change | vs. peak |
|---|---|---|---|
| Jefferson | $341,000 | +7.3% | At peak |
| Fort Atkinson | $305,000 | +5.9% | At peak |
| Lake Mills | $426,000 | +3.2% | At peak |
| Johnson Creek | $413,000 | +5.4% | At peak |
| Palmyra | $369,000 | +4.7% | At peak |
| Sullivan | $435,000 | +4.6% | At peak |
| Waterloo | $318,000 | +3.9% | At peak |
| Helenville | $442,000 | +4.3% | At peak |
| Lake Koshkonong | $209,000 | -13.7% | -45.1% |
| Lake Ripley | $436,000 | +2.3% | At peak |
Deadline and where to file
Lake Koshkonong values are set by the local municipal assessor. Give the Board of Review clerk notice of intent to object at least 48 hours before the Board's first meeting, and file Form PA-115A before or during the first two hours of that first meeting. The Board must meet during the 45-day period starting the fourth Monday in April, and at least 7 days after Open Book.
Reading this in fall 2026? The 2026 Board of Review window has closed. Your next chance is the 2027 Board of Review, which starts around the fourth Monday in April 2027. Watch for your Notice of Changed Assessment (mailed at least 15 days before the meeting, 30 in revaluation years) and the Open Book notice. Exact dates are set by your municipality. If you already objected at the 2026 Board and paid your tax, an excessive assessment claim for 2026 taxes is due to your municipality by January 31, 2027.
The Jefferson County guide covers the full Wisconsin appeal process: forms, fees, hearing levels and what happens next.
Building a Lake Koshkonong case
Averages explain why a case might work. The decision turns on evidence about one property. Lake Koshkonong is part of the Watertown-Fort Atkinson metro, but your evidence should be local. Sales a few streets away usually beat sales across the metro.
- The assessor's value is presumed correct. Prove it is too high with recent arm's-length sales of your home or comparable homes in your municipality.
Get your Lake Koshkonong appeal report
Start with your address. Vulorean checks your assessment against recent comparable sales and builds a value report you can bring to your Wisconsin appeal. Eligible reports are free during launch; an account is required and local filing fees are separate.
Check my property and get a report →Vulorean was built for California first. Wisconsin forms, deadlines and filing rules vary, so confirm them with your local office before filing. If something in your report looks wrong, email support@vulorean.com and we'll get it fixed.
Home values: Zillow Home Value Index (ZHVI), all homes, mid-tier, smoothed and seasonally adjusted, through August 2026, from Zillow Research. Rules: Wisconsin DOR 2026 Guide for Property Owners (pb060), Wisconsin Statutes 70.47, Board of Review, Wisconsin DOR Board of Review filing objections and forms, Form PA-115A. Vulorean is an independent service, not a government office. Confirm dates and forms with your local office.