a. One who sits as assistant or adviser to a judge or magistrate; esp. a skilled assistant competent to advise on technical points of law, commercial usage, navigation, etc.
b. One who assesses taxes.
c. One who officially estimates the value of property or income for purposes of taxation.
Oxford English Dictionary
In some states, especially Massachusetts, the tax assessment of a town would determine how many state representatives could be elected.
1801 - 1825: Delaware, Massachusetts, New York, Pennsylvania, Rhode Island
Office Scope: County / City / Hundred / District / Borough
Role Scope: County / Hundred / Ward / District / Borough