See Full Constitution
Article VII

Section 2. County Territory, Boundaries and Seats

(a) The General Assembly shall provide by law for the formation, consolidation, merger, division, and dissolution of counties, and for the transfer of territory between counties.
(b) County boundaries shall not be changed unless approved by referendum in each county affected.
(c) County seats shall not be changed unless approved by three-fifths of those voting on the question in a county-wide referendum.