Property Tax Appeals in Sonoma County, California
Sonoma County's Assessment Appeal Application states a $30 non-refundable processing fee to be paid at the time of filing, by check or money order only, payable to the County of Sonoma. The county's Assessment Appeals Board directs applicants to print, sign, and submit the completed application, and its posted filing pages do not describe an online e-filing system, so the application is filed by mail or in person at the Board's Santa Rosa office. The county's Assessment Appeals page also discloses that, due to recent years' market conditions, applicants can expect roughly a 6-18 month wait for a hearing, though state law allows up to two years. FairPath can organize an owner-managed comparison table, condition exhibits, official links, and a filing checklist. It does not file the application, select the owner's opinion of value, pay the fee, negotiate with the Assessor, or appear at the hearing.
Assessment context: Begin with the Assessor's parcel record and confirm whether the dispute concerns the January 1, 2026 lien-date value on the regular roll, a supplemental assessment tied to a change of ownership or new construction, or an escape assessment discovered after the fact. Sonoma County spans the urbanized Santa Rosa and Petaluma corridors, incorporated cities such as Sonoma, Healdsburg, and Rohnert Park, and extensive unincorporated wine-country, coastal, and rural residential areas. A vineyard parcel a few miles from a subdivision lot is not automatically comparable. Zoning, agricultural use, wildfire-hazard exposure, and site access should be confirmed against the Assessor's record rather than assumed from a map.
Filing process: Download the Assessment Appeal Application and Instructions, form BOE-305-AH, from the Assessment Appeals Board's Filing an Application page, or request a paper copy from the Board office. Provide the parcel or assessment number, the type of assessment being appealed, and an opinion of value, and include the $30 non-refundable processing fee by check or money order payable to the County of Sonoma; the form warns that an application without a stated opinion of value will be rejected. Print, sign, and mail or deliver the completed application to the Assessment Appeals Board, 575 Administration Drive, Room 100A, Santa Rosa, CA 95403-2815. An application may be amended until 5:00 p.m. on the last day it could have been timely filed. Property taxes remain due while the appeal is pending.
Evidence to review: Sonoma County's application instructions describe a Revenue and Taxation Code Section 1606 exchange of information, which either the applicant or the Assessor's Office may request once the assessed value exceeds $100,000, and note that a list of property transfers may be inspected at the Assessor's office for a fee not to exceed $10. Build a comparable-sales table showing sale date, price, parcel, neighborhood, lot size, living area, age, and condition, and prioritize sales close to the January 1, 2026 lien date; California generally excludes comparable sales occurring more than 90 days after that date. For wine-country, coastal, or wildfire-interface parcels, document access limitations, agricultural use, or condition facts with dated photographs or inspection findings rather than relying on a distance-only comparison.
Current deadline guidance: 2026 regular assessment appeals: July 2 through November 30, 2026. Sonoma County's Assessment Appeals Board page states that for a Regular Assessment appeal, the filing period is July 2nd through November 30th of the current year, consistent with the California State Board of Equalization's certified county filing-period table. Supplemental and escape assessments instead run on a notice-specific 60-day clock from the mailing or postmark date on the notice, whichever is later.
Sonoma County's 2026 regular filing period for Regular Assessment appeals runs July 2 through November 30, matching the state's extended deadline group.
The Assessment Appeal Application requires a $30 non-refundable processing fee, payable by check or money order only to the County of Sonoma, at the time of filing.
Sonoma County's posted filing pages describe a paper application mailed or delivered to the Board's Santa Rosa office; an online e-filing system is not described.
The Assessment Appeals Board discloses an approximately 6-18 month wait time for a hearing due to application backlog, though state law allows up to two years.
Official filing authority: Sonoma County Assessment Appeals Board. https://sonomacounty.gov/administrative-support-and-fiscal-services/board-of-supervisors/services-and-information/assessment-appeals/filing-an-application
Source: Sonoma County Board of Supervisors Department, Filing an Application | Assessment Appeals, https://sonomacounty.gov/administrative-support-and-fiscal-services/board-of-supervisors/services-and-information/assessment-appeals/filing-an-application. Reviewed 2026-09-22.
Source: Sonoma County Board of Supervisors Department, Common Assessment Types and Filing Deadlines, https://sonomacounty.gov/administrative-support-and-fiscal-services/board-of-supervisors/services-and-information/assessment-appeals/common-assessment-types-and-filing-timelines. Reviewed 2026-09-22.
Source: Sonoma County Board of Supervisors Department, Assessment Appeals, https://sonomacounty.gov/administrative-support-and-fiscal-services/board-of-supervisors/services-and-information/assessment-appeals. Reviewed 2026-09-22.
Source: California State Board of Equalization, Letter to Assessors 2026/023: 2026 Assessment Appeal Filing Periods, https://boe.ca.gov/proptaxes/pdf/lta26023.pdf. Reviewed 2026-09-22.
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