These counties together contain 564 municipalities, or administrative entities composed of clearly defined territory; 253 boroughs, 52 cities, 15 towns, 240 townships, and 4 villages.

In the wake of the 1964 decision by the Supreme Court of the United States in Reynolds v. Sims, establishing the one man, one vote principle that state legislative districts must be approximately equal in size, David Friedland filed suit in New Jersey Supreme Court on behalf of two union leaders, challenging a system under which each county was represented by a single member in the New Jersey Senate.

[9] The Supreme Court ruled unanimously that it was unconstitutional for the senate to adopt a weighted voting system unilaterally.

[9][10] In 1966, the constitution was amended to establish 40 districts statewide, each represented by one senator and two assembly members, without relation to county boundaries.

[11] The Federal Information Processing Standard (FIPS) code, used by the United States government to uniquely identify counties, is provided with each entry.