At the regular meeting in January, preceding any general election, the board of commissioners must district their county into three (3) districts, as nearly equal in population as may be, to be known as county commissioners’ districts, numbers one (1), two (2) and three (3) respectively; provided, that when a new county shall have been created, or the boundary lines of a county shall have been changed, then the board of commissioners of such county may district their county at any general or special meeting of such board.