(1) All cities, which at the last federal census had, or now have, a population exceeding two thousand five hundred (2,500) inhabitants shall be deemed cities of the first class.
(2) All cities which, at any future federal census, or any census which may be taken in pursuance of the laws of this state, shall be found to have a population of two thousand five hundred (2,500) inhabitants shall thereafter be deemed cities of the first class.