Founded in 1963, the zoo was originally a showcase for animals indigenous to the New York metropolitan area but currently features species from every continent except Antarctica.

[2] Located adjacent to the Richard J. Codey Arena, the former practice home of the New Jersey Devils, the zoo is open year-round, weather permitting.

[2] It was originally opened seasonally and had a Hans Christian Andersen "storybook theme," with such exhibits as "a giant piggy bank, the ABC house, [and] the pirates’ ship".

New facilities included the Essex County Animal Hospital on zoo grounds, and a new 11,000-square-foot (1,000 m2) entrance/administrative complex with a 4,000-square-foot (370 m2) reptile center, classrooms, and an auditorium.

[3] Residents of Essex County have lobbied for expansion of the zoo to cease, citing traffic congestion and disruption of the surrounding South Mountain Reservation.

In July 2019, Essex County officials announced the construction of a proposed amphitheater, grizzly bear exhibit, and overnight camping.

[5] Essex County officials reported in September 2019 that as a result of the backlash, the amphitheater was scaled back, though no exact details were released.

When the 4,000-square-foot (370 m2) reptile center opened, it contained a pair of nine-foot-long "black dragons", a species of monitor lizard which was discovered in Malaysia in 2005 and has yet to receive a scientific name.

After Amazing Asia was renovated in September 2022, the exhibit allowed the zoo's red pandas and clouded leopards to have more room to roam.

[14] In addition the exhibit contains elands, bongos, a pair of Abyssinian ground hornbills, White-faced whistling ducks, ostriches, and bonteboks.

This exhibit features an 82,000-gallon pool for California sea lions and a 1,600-gallon touch tank for sting rays and small sharks, along with space for education programs and special events.

In April 2015, the railroad received a third C. P. Huntington locomotive from a Livingston resident as part of a program to commemorate the 150th anniversary of Abraham Lincoln's death.

[2] In May 2022, it was renamed as the “Essex County Barry H. Ostrowsky Animal Wellness Center”, in honor of the president and CEO of RWJBarnabas Health.