(a) In a county with a population of more than 75,000, the county government shall classify all positions in its sheriff's department and shall specify the duties and prescribe the salary for each classification.
(a-1) A county government in a county that has a population of more than 7,500, is located on an international boundary, and contains no incorporated territory of a municipality may classify all positions in its sheriff's department and may specify the duties and prescribe the salary for each classification.
(b) A member of the sheriff's department who is required to perform the duties of a particular classification is entitled to be paid the salary prescribed for that position during the time the member performs those duties.