Commonly Asked Questions What is ad valorem? A tax based upon the assessed value of property, used interchangeably with “property tax”; derived from a Latin phrase meaning, “according to worth.”   Property taxes are determined by multiplying the rate of taxation expressed in mills (0.001) times the non-exempt value of property or taxable value. What is a mill (also known as millage rate)? A mill, as used with ad valorem taxes, is the rate that expresses the dollars of tax per