Your assessment should reflect the approximate market value of your property as of July 1 of the previous year. If you believe your assessment is incorrect, you have the right to file a grievance petition. This can be done two ways; formally and informally.
The Assessor’s office has put together a very helpful packet (PDF) that explains, in detail, the whole grievance process.
The Grievance informal review period is from May 1st to the 3rd Tuesday in June. You could arrange an appointment to speak to someone at the assessor’s office. At that time, you can provide any documentation you have, to prove why you feel your assessment may be incorrect. A contract of sale, a Current Market Analysis (CMA) from a Realtor or recent appraisal would be your best proof. Also, keep in mind that the Assessment staff is available throughout the year to discuss your assessment or any other questions you may have regarding your property.
The formal process starts between June 1st and the 3rd Tuesday in June. That is when the owner submits the grievance form (RP-524 (PDF). If you would like to present your case in front of the Board of Assessment Review, you can schedule a time to appear on the 3rd Tuesday in June. Regardless whether you appear or not, your application will be reviewed by the Board of Assessment Review in deliberative session throughout the summer, and a decision will be made (and mailed) by September 15th of that year.