Upon adoption of the optional County Sheriff's Civil Service Law of 1974 by a two-thirds majority vote of the county legislative body, the county legislative body selects three people to serve on a civil service board. These three members must be at least 18 years of age, be residents of the county and cannot hold any elected or appointed office within the county. The term of office is three years except for the initial appointments for one, two and three years to create a staggered system. This board may or may not be compensated at the discretion of the county legislative body. The board adopts a classification plan, determines the requirements of each position and performs other duties specified in this optional law. Some counties have similar boards created by private act. T.C.A. § 8-8-401 et seq.