[1][2] As of the 2020 United States census, the district had a population of 235,539, of whom 194,652 (82.6%) were of voting age.

During the period of time after the 1964 Supreme Court decision in Reynolds v. Sims and before the establishment of a 40-district legislature in 1973, the 9th district encompassed the entirety of Union County.

Republicans Nicholas S. LaCorte, Frank X. McDermott, and Matthew John Rinaldo won the 1967 election though LaCorte would resign on December 7, 1970 to become a tax appeals judge.

[9][10] Democrat Jerry Fitzgerald English would win a 1971 special election to complete LaCorte's term.

[16] Jackson Township and Plumsted Township and the northern Burlington municipalities were shifted out of the 9th in the 1991 redistricting; more of southern Burlington was added including Tabernacle, Woodland, Washington, and Bass River townships and Egg Harbor City in Atlantic County were also added to the district for this decade.