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Tax Payer Information

Tax Payers Rights

If you disagree with the valuation placed on your property, you may take the matter up with the Assessor to see if that office will change the valuation. Additionally, the Board of Supervisors has established several Assessment Appeals Boards for the purpose of resolving valuation problems. Appeals on regular assessments must be filed each year between July 2 and November 30 (valuation information is available July 1 at the Assessor's Office). Appeals on corrected assessments, escaped assessments (assessments that did not take place when they should have), or supplemental assessments must be filed no later than 60 days from the date of notice or the postmark of that notice, whichever is later.

If you choose to appeal your assessment, you should still pay your tax installments in full by the appropriate deadlines; otherwise, you may incur penalties while the case is in appeals. If your appeal is granted, a refund will be issued to you.

Appeals applications and further information about the appeals process can be obtained by calling (707) 565-2241 or writing to: Assessment Appeals Board, 575 Administration Dr., Room 100A, Santa Rosa, CA 95403, or you may visit the Assessor's website.

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New Owner Information

As a new owner, you are responsible for any taxes that were not paid as of the time escrow closed. Even though taxes are prorated between the buyer and seller during escrow and proper credit is given to each, the actual taxes may not have been paid to the Tax Collector by that time. You should read your escrow papers and/or title report to determine if any portion of the annual taxes were paid by the previous owner before the close of escrow.

Annual tax bills, which can be paid in two installments, are mailed once a year by November 1. Since the bill contains payment stubs for both installments, this is the only bill regularly mailed each year by the Tax Collector. Depending on when the ownership change is placed on the tax roll, the annual tax bill could be sent either to the previous owner or directly to you. If there are any remaining unpaid taxes, and if you did not receive an annual tax bill from either the previous owner or the Tax Collector, you should contact the Tax Collector immediately and request one. It is your responsibility to obtain the bill. State law stipulates that failure to receive a bill does not permit the Tax Collector to excuse penalties on late payments.

In addition to annual taxes, you will probably be responsible for paying Supplemental Property Taxes. Any time property is sold or improved, the value of the property is reassessed. If the property has been reassessed at a higher value, you will receive one or more supplemental tax bills in addition to the annual bill mentioned above. (For more information on supplemental tax bills, please read our section on Supplemental Property Taxes.) If the property has been reassessed at a lower value, you will receive a refund.

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Exemption and Assistance Programs

Through the Assessor's Office you can apply for the homeowner's property tax exemption, veteran's exemption, or church and welfare exemption. These programs allow for assessment exemptions that result in tax savings. For further information, contact the Assessor's Office at (707) 565-1888.

In addition, the State of California administers programs that provide property tax assistance and postponement of property taxes to qualified homeowners and renters who are 62 or older, blind, or disabled. For information on the State's Homeowner or Renter Assistance Program, call the Franchise Tax Board at (800) 868-4171. For information on the Property Tax Postponement Program, call the California State Controller's Office at (800) 952-5661.

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Secured Property Taxes

Property taxes are collected by the County, although they are governed by California State law. The Tax Collector of Sonoma County collects taxes on behalf of the County, the County's 9 incorporated cities, over 40 school districts, and all other taxing agencies located in the County, including over 70 special districts (e.g., flood control districts, sanitation districts). Upon collection of these taxes by the County, appropriate distribution is made to the various taxing agencies.

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Unsecured Property Taxes

The Sonoma County Treasurer Tax-Collector is charged with collection of unsecured taxes. Unsecured property taxes are taxes on un landed property such as:

  • Business Equipment and Leasehold Improvements
  • Mobile homes that are not attached to a foundation (see our Frequently Asked Questions section for more information on Mobile homes).
  • Aircraft and Vessels (including fishing vessels)
  • Cabins on leased or Publicly Owned Property
  • Leased Business Equipment
  • Possessory Interest (lessees of publicly owned properties such as marinas, airports, grazing rights, and housing on publicly owned lands.)
  • Unsecured Supplemental (real estate tax billed to a former owner following the close of escrow, for differences in assessed value resulting in an additional tax computed for a prior period of ownership. See Supplemental Property Taxes.)

Unsecured taxes are computed by the County Assessor, who determines the value of the property and transmits that information to the County Auditor. The Auditor computes the amount of tax (see Computation of Taxes, above) and transmits that information to the Tax Collector, who prepares the bill for the taxpayer and collects the tax. If you have questions regarding valuation of your property, please contact the Sonoma County Assessor's Office at (707) 565-1888.

Unsecured Property taxes are levied on property as it exists on January 1st at 12:01 AM. Tax bills are prepared and mailed in July of each year. Unsecured taxes must be paid on or before August 31st unless otherwise stated. The obligation to pay unsecured taxes rests with the assessed owner of record on the lien date (January, 12:01 AM.) The disposal of property AFTER the lien date does not relieve the assessed owner from the obligation to pay unsecured taxes. Delinquent unsecured taxes are subject to collection enforcement. The Tax Collector cannot pro-rate taxes.

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Supplemental Property Taxes

California State law requires the reassessment of property as of the first day of the month following an ownership change or the completion of new construction. What is meant by new construction is any substantial addition to real property (e.g., adding a new room, pool, or garage) or any substantial alteration which restores a building, room, or other improvement to the equivalent of new (e.g., completely renovating an outdated kitchen). In most cases, this reassessment results in one or more supplemental tax bills being sent to the property owner in addition to the annual property tax bill.

Property owners who have impound accounts should contact their lender regarding payment of supplemental tax bills.

Most changes in ownership caused by the sale of property result in reassessment. However, interspousal transfers, the transfer, sale, or inheritance of property between parents and their children, and the addition of joint tenants do not result in the reappraisal of property values.

Furthermore, homeowners over the age of 55 years who sell their principal residence and purchase a replacement dwelling within two years that is of equal or lesser market value and is located in the same county are eligible to transfer the pre-sale assessed value of their original property to the replacement dwelling. For further information, please contact the Office of the Assessor at (707) 565-1888.

The Assessor first determines the new value of the property based on current market values. The Assessor then calculates the difference between the new value (set at the time of purchase or completion of new construction) and the old value (set on January 1 of the previous fiscal year). The result is the supplemental assessment value. Once the new assessed value of your property has been determined, the Assessor will send you a notification of the amount to be assessed.


  • New value at date of purchase or completion of new construction $120,000
  • Assessed value for current fiscal year $100,000
  • Supplemental assessment value will be $20,000

This reassessment usually results in an increase in property value, in which case your supplemental taxes will be calculated by the Auditor-Controller based on the change in value, and one or more supplemental tax bills will be created and mailed to you by the Tax Collector. However, in some instances the reassessment results in a reduction in value, in which case a refund will be prepared by the Auditor-Controller and mailed to you. A reduction in value will not reduce the amount due on the annual tax bill. The annual tax bill must be paid in the amount originally billed.

The date on which supplemental bills become delinquent varies depending upon when they are mailed by the Tax Collector. As outlined in Figure 2 below, if the bill is mailed between July 1 and October 30, the taxes become delinquent at 5 p.m. on December 10 for the first installment and 5 p.m. on April 10 for the second installment (the same delinquency schedule as for annual tax bills mailed in November).

Figure 2

Bill mailed between
July 1 and October 30
1st installment delinquent:
December 10
2nd installment delinquent:
April 10

If the bill is mailed between November 1 and June 30, the delinquency dates - which are printed on the bill - are determined as follows: The first installment is delinquent at 5 p.m. on the last day of the month following the month the bill was mailed; the second installment is delinquent at 5 p.m. on the last day of the fourth month after the first installment delinquency date (see Figure 3).

Figure 3

Bill mailed between
November 1 and June 30
1st installment delinquent:
Last day of the month following the month bill was mailed
2nd installment delinquent:
Last day of the 4th month after the 1st installment became delinquent

Penalties of 10% are added to any installment that is not paid on time, and an additional $20 charge is added to a late second installment.

The supplemental tax bill is sent in addition to the annual tax bill and both must be paid as specified on the bill. For information on the annual tax bill, see our section on Paying Your Property Taxes. For more information on supplementary tax bills, see our Frequently Asked Questions section.

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