If the assessee name or the property being assessed is incorrect, contact the Assessor’s Office at (925) 313-7600. If it's between the dates of July 2 and November 30 contact the Assessment Appeals Board.
In the meantime, you must still pay the taxes by the due date in order to avoid penalties, liens and enforced collections. Should the taxes be reduced later, a refund will be issued.
Information about the appeals process can be obtained by calling (925) 335-1901 or writing to:
Clerk of the Assessment Appeals Board
651 Pine St., Room 106
Martinez, CA 94553
If the tax rate is incorrect, contact the Auditor’s Office, Property Tax Division, at (925) 646-2236.