Most municipalities do not assess properties at 100% of value. You cannot simply know what market values the assessor is assigning to your property. In fact, the only way to calculate the market value from the assessment is to know the ratio of assessment to market value for your type of property in that municipality. The ratio changes every year to further frustrate the property owner.
New assessments are to be promulgated on January 2, 2016 for Nassau County and May 1, 2016 for Suffolk County. The villages and cities have different dates and, of course, different assessments and ratios. Watch your mail for any changes in the assessment and have an expert (not the municipal assessor) determine if you are being over assessed.