County filing guide
How to appeal your property tax in Sonoma County
Regular decline-in-value appeals. Supplemental and escape assessments have different deadlines.
Filing options
Filing instructions
Informal review with the Assessor
The Assessor's website says the 2026–27 informal Prop 8 review period is closed, checked October 6, 2026. The reference steps below explain where to check the current status and contact staff. A separate formal appeal remains available during its filing period; an informal inquiry does not extend that deadline.
Open the Assessor's Temporary Decline in Market Value page and check the current review-period notice. For questions, contact the Real Property team at [email protected] or 707-565-1888.
Check the current informal review-period notice. Have your parcel number, property address, current assessed value, and your opinion of market value as of January 1 ready. Explain why you believe the assessment is too high, using your comparable sales and any relevant property-condition evidence.
Ask the Assessor which current-year form or supporting documents to use, how to submit them, and whether a request can still be accepted. Follow the instructions they provide and keep a copy of your request.
If the issue is unresolved as the formal deadline approaches, file the separate Assessment Appeal Application below by November 30, 2026. Do not wait for an informal response past that deadline.
Formal appeal by mail or in person
The 2026 regular appeal filing period is July 2, 2026–November 30, 2026. Sonoma's published application requires a printed, signed form and a $30 non-refundable processing fee.
Open the county's Filing an Application page and download Assessment Appeal Application and Instructions. The application PDF is also available directly.
Download the formal application and instructions. Read the instructions and complete the applicant, property, and value sections. Use the parcel number and assessed value from your tax bill or assessment notice, and enter your own supported opinion of value. Complete the applicable assessment type, reason for appeal, and remaining questions.
Print, review, sign, and date the application. Include a $30 check or money order payable to County of Sonoma. Do not attach your hearing evidence to the application; retain it for the hearing process.
Mail or deliver the signed application and fee to Assessment Appeals Board, County of Sonoma, 575 Administration Drive, Room 100A, Santa Rosa, CA 95403-2815 during the filing period. Allow enough time for delivery before November 30, 2026 and keep a complete copy and delivery record.
Watch for correspondence from the Clerk and follow any instructions about your application or hearing. Continue paying property taxes when due while the appeal is pending.
After you file
Informal review
Confirm the informal review process with the county before submitting a request.
Formal appeal
Keep a copy of your application and filing confirmation. Watch for notices from the Clerk of the Board and follow the county’s instructions for any hearing.
Open my appeal plans →Contacts & sources
Clerk of the Board
Runs the formal appeal
707-565-2241 · appeals page ↗
575 Administration Drive, Room 100A, Santa Rosa, CA 95403-2815
This guide covers the regular decline-in-value appeal; supplemental or escape assessment notices follow different deadlines. Every date and fee here was checked against official sources, listed below with the date checked. If the county's page ever differs from this guide, follow the county's page.
Sources
Informal sources
- Sonoma County Assessor — office contacts and assessment-roll access — checked directly October 6, 2026.
- Temporary Decline in Market Value — checked directly October 6, 2026.
- Scope: residential decline-in-value discussion with the Real Property team. The live county page, checked October 6, 2026, confirms the 2026–27 informal period is closed and directs owners to formal appeals. Its exact closing date, a current residential request form and a submission portal were not verified. Older residential and Business Property sample forms are not used as current filing instructions. The annotated notice is beneath informal Step 1; no request was submitted.
Formal sources
- Filing an Application — county instructions — checked directly October 6, 2026.
- Sonoma application and instructions, BOE-305-AH Rev. 12 (05-24) — signed paper submission, fee, payee, address, and application requirements.
- Sonoma Assessment Appeals — one application for each assessment/year and continued tax payments.
- California BOE 2026 county filing periods — July 2–November 30, 2026.
- Scope: regular annual assessed-value appeals. Supplemental, escape, and other special assessments have separate rules. The published county process is a downloadable paper application; no complete electronic filing route was verified.
- County Assessor and Clerk pages were rechecked directly in the browser October 6, 2026. Two annotated screenshots were added beneath the corresponding first steps; later paper-form steps remain document-backed. No application was submitted.
Formal appeal window
- https://www.boe.ca.gov/proptaxes/pdf/lta26023.pdf · “The regular appeals filing period in each county will begin on July 2, 2026, and will end on September 15, 2026, for those counties where the Assessor mails assessment notices to all taxpayers with property on the secured roll by August 1, 2026. For counties where assessment notices are not mailed by August 1, 2026, the filing period is extended to November 30, 2026.” (checked July 10, 2026)
Filing fee
- https://www.sonomacountylawlibrary.org/Main%20County%20Site/Administrative%20Support%20&%20Fiscal%20Services/BoS/Documents/Assessment%20Appeals/AAB-Application-Instructions.pdf · “$30 Non-Refundable Processing fee to be paid at time of filing. (Checks or Money order ONLY. Payable to County of Sonoma)” (checked July 11, 2026)
Filing address
- https://www.sonomacountylawlibrary.org/Main%20County%20Site/Administrative%20Support%20&%20Fiscal%20Services/BoS/Documents/Assessment%20Appeals/AAB-Application-Instructions.pdf · “Please print, sign and submit this form to: Assessment Appeals Board County of Sonoma 575 Administration Drive, Room 100A Santa Rosa, CA 95403-2815” (checked July 11, 2026)
Filing channels
- https://sonomacounty.gov/Main%20County%20Site/Administrative%20Support%20%26%20Fiscal%20Services/BoS/Documents/Assessment%20Appeals/AAB-Application-Instructions.pdf · “Please print, sign and submit this form to: Assessment Appeals Board County of Sonoma 575 Administration Drive, Room 100A Santa Rosa, CA 95403-2815” (checked October 7, 2026)
Common questions about appealing in Sonoma County
When is the deadline to appeal in Sonoma County?
The deadline to file a formal appeal in Sonoma County for the 2026-27 tax year is November 30, 2026. Filing opened July 2, 2026.
What does it cost to file an appeal in Sonoma County?
The county filing fee for a formal appeal is $30.
Informal review or formal appeal: which one first?
We have not established whether Sonoma County offers a separate informal review. The formal appeal is an application to the Clerk of the Board, due November 30, 2026. See the Assessor's review request page ↗.
Which form do I file, and where?
The formal appeal uses the state's application form, BOE-305-AH ↗.
Sonoma County accepts the formal appeal by mail or in person.
Mail it to the Clerk of the Board at 575 Administration Drive, Room 100A, Santa Rosa, CA 95403-2815.
Check the Clerk of the Board's appeals page ↗ or call 707-565-2241 before you file.
How long does an appeal take?
You get written notice at least 45 days ahead, hearings are open to the public (you can watch one first), and boards are expected to decide within two years of filing. You can still settle at any point before your date.
Do homeowners actually get their assessments lowered?
1,632 homes in Sonoma County had temporarily reduced assessments in tax year 2025-26.