If a vacancy shall occur in the office of a commissioner, the sheriff, with the approval of the majority of the members of the county board, shall appoint a suitable person to serve the unexpired portion of that commissioner's term. If the sheriff fails to appoint a person to fill the vacancy within thirty (30) days, the chair of the county board shall appoint a person to fill the unexpired portion of the term, with the approval of a majority of the members of the county board. (1977 Code ch. 20)