The first of nine jails on violence-plagued Rikers Island is set to close by summer, the city’s Correction Department announced Tuesday.

The jail — known as the George Motchan Detention Center, where about 600 men are all awaiting trial — was picked to go first because the building is deteriorating with maintenance problems including a bad sewer system, and the inmate population is at only 50 percent capacity, said Correction Commissioner Cynthia Brann. She said inmates would be moved elsewhere, as would the 1,000 personnel assigned to the jail, known as GMDC.

The closure is part of Mayor Bill de Blasio’s 10-year estimate for shuttering the complex, which a blue-ribbon panel has said can and should be closed far sooner.

Elizabeth Glazer, who oversees de Blasio’s Office of Criminal Justice, said the jail building could be closed because of a drop in the number of inmates — a record low, below 9,000 across the city in December, the first time since 1982. It was 8,705 on New Year’s Day. She attributed the decline to the NYPD choosing to make fewer arrests for lower-level offenses, prosecutors seeking jail sentences less often, and “New Yorkers are simply committing fewer crimes.”

De Blasio has said the island complex wouldn’t close completely until the citywide jail population dipped below 5,000.

Opened in 1971, the jail made headlines in December when Colin Kaepernick — the former San Francisco 49ers quarterback who sparked controversy by kneeling in protest during the national anthem — visited to meet with inmates.

It also held Abel Cedeno, 18, the gay, allegedly bullied teen charged with killing a classmate and wounding another at a Bronx school in September, before Cedeno was released on bail in November.

Brann would not say whether the jail could be reopened if the jail population goes up — a development she doesn’t anticipate. She said that no guards would be laid off, but she hoped overtime hours would go down.

Initially called the Correctional Institution for Women, GMDC was named later after a guard fatally shot in the line of duty. In 1988, it began housing only men when another jail for women opened elsewhere on Rikers.

In 1990, GMDC was used to quarantine inmates during an island-wide tuberculosis outbreak.

In March, de Blasio reversed his opposition to closing Rikers, which the U.S. Justice Department has said is characterized by corruption and a “deep-seated culture of violence.”

But he has frustrated pro-closure activists by insisting that Rikers can’t be closed until 2027 — long after he’s out of office — and deferring to a future mayor the politically fraught choice of where in the boroughs to open replacement lockups and even whether to actually go through with shuttering the complex.

In October, the state’s former chief judge, Jonathan Lippman, who headed a panel that recommended closure, wrote in an Op-Ed in amNewYork that the timeline could be shorter and that de Blasio’s plan “won’t get us across the finish line.”

The activists lament that the antiquated design and deteriorating plant at Rikers’ jails prevent efficient jail supervision. The island, located between the Bronx and Queens in the East River, is accessible only by public bus and is hard to reach for families seeking to visit loved ones. And it’s far away from the courts, where inmates, nearly all of whom haven’t been convicted, must be bused to and from hearings.