(1) As used in this section, "single-family limit" means the number of individuals allowed to occupy each residential unit that is recognized by a land use authority in a zone permitting occupancy by a single family.
(2) A county may not adopt a single-family limit that is less than:
(a) three, if the county has within its unincorporated area:
(i) a state university;
(ii) a private university with a student population of at least 20,000; or
(iii) a mountainous planning district; or
(b) four, for each other county.