STATEMENTS. This claim may be used to file for the Homeowners' Exemption for the Assessment Roll and the Supplemental Assessment Roll. Total of 103 forms are available for Contra Costa County for 2024.Download PDF BOE-266 REV. Exemption forms are due June 30th each year. Once forms are filed exemption is automatically renewed each year. Contact the city where the business will be located, or the Tax Collector if the business will be located in an unincorporated area of Contra Costa County. A residency classification is made at the time of application. The standard for a particular county and family size includes both housing and utilities allowed for a taxpayer's primary place of residence. The department may ask you to fill out a Legal Residence (Domicile) ​Questionnaire​ to determine your domicile. Applicable Laws and Rules.