(a) The governing authority of any county of this state or the General Assembly may create in and for those counties in which it deems necessary or advisable the office of county manager and may vest in such office powers, duties, and responsibilities of an administrative nature. The qualifications, method of selection, appointment, compensation, tenure, and such other related matters pertaining to the office of county manager shall be provided for by the governing authority of the county.

(b) Nothing in this Code section shall pertain to consolidated governments which include all the area within any county.

(c) This Code section shall not apply to any county having a population of more than 500,000 according to the United States decennial census of 1990 or any future such census.