(1) Every city having a population of 10,000 or more is a city of the first class.
(2) Every city having a population of less than 10,000 and more than 5,000 is a city of the second class.
(3) Every city having a population of less than 5,000 and more than 1,000 is a city of the third class.
(4) Every municipal corporation having a population of less than 1,000 and more than 300 is a town.