WHITE HALL, Ark.—When it was built, U.S. Army planners envisioned creating a city within the Pine Bluff Arsenal to house soldiers and amenities for those working there.

Now the base’s namesake city finds itself facing losing the decontamination jobs and an economic engine for the dwindling Arkansas city.

Pine Bluff, just south of Little Rock, now has a population of more than 51,000. That’s down from the city’s high of 57,389 in 1970, just after former President Richard Nixon ordered a ban on chemical weapons production.

In the time since, Pine Bluff saw residents leave over crime concerns and a growing unemployment rate. If the city’s population drops, it could lose needed government dollars distributed on a per capita basis. Under state law, the city also would have to change the way it elects its city council members—largely limiting them to two-year terms as opposed to four.

Worries about population forced former Pine Bluff Mayor Jerry Taylor to push for annexing four state Department of Correction prison facilities into the city limits in 1999.

The largest employers in the Pine Bluff area remain the arsenal, the National Center for Toxicological Research, the Jefferson Regional Medical Center and the city’s paper mills, said Mayor Carl A. Redus Jr. He said losing any of those could be a death knell for the city.

“It is absolutely first and foremost at the top of the list,” Redus said.