For legislative purposes, counties are classified as follows based upon their population as ascertained by the most recent federal decennial census:
a. First class--counties having a population of more than 550,000 and a population density of more than 3,000 persons per square mile;
b. Second class-- all other counties having a population of more than 200,000 except such counties bordering on the Atlantic ocean;
c. Third class--counties having a population of not less than 50,000 but not more than 200,000 except such counties bordering on the Atlantic ocean;
d. Fourth class--counties having a population of less than 50,000 except such counties bordering on the Atlantic ocean;
e. Fifth class--counties bordering on the Atlantic ocean having a population of more than 125,000;
f. Sixth class--counties bordering on the Atlantic ocean having a population of not more than 125,000.