First day to file application for assessment reduction. August 31, Regular roll unsecured tax bills due.Obtain forms from either the County Assessor or the Clerk of the Board in the county where the property is located). When mailing a payment, include the payment coupon and check or money order in the return courtesy envelope provided. Can the county assessor prorate assessments or taxes between the buyer and seller of taxable personal property? The owner of a shortterm rental filing form BOE571STR will be required to report the year acquired and the original cost of personal property. The Property Appraiser's Office is responsible for maintaining and correcting billing information for each property record. Please choose one of the following tax types. County of Santa Clara. Department of Tax and Collections.