In the case of a full-time district health department the cost of operating and maintaining the department, over the estimated moneys available from surpluses, grants, and donations, shall be apportioned by the district board of health among the counties comprising the district. Apportionment shall be on the basis of population, as determined by the State Department of Health in its most recent mid-year census estimate, of each county in proportion to the total population of all counties comprising the district.
SDCL 34-3-23