(a) Except as provided in Section 4-2001, where assistant State‘s Attorneys are required in any county, the number of such assistants shall be determined by the county board, and the salaries of such assistants shall be fixed by the State’s Attorney subject to budgetary limitations established by the county board and paid out of the county treasury in quarterly annual installments, on the order of the county board on the treasurer of said county. Such assistant State’s Attorneys are to be named by the State’s Attorney of the county, and when so appointed shall take the oath of office in the same manner as State’s Attorneys and shall be under the supervision of the State’s Attorney.
     (b) The State’s Attorney may appoint qualified attorneys to assist as Special Assistant State’s Attorneys when the public interest so requires.