He Went to Jail on Minor Charges. He Left in a Coma.

A spokesman for New Jersey’s U.S. attorney’s office had no comment.

Leaders of the union that represents supervisors at the Essex County jail said that administrators and county officials had ignored repeated warnings that the facility was growing increasingly violent.

Paramedics or emergency medical technicians were called to the jail 169 times between January and June to treat either officers or detainees, up from 99 times during the same period last year, according to documents released by the union, the Fraternal Order of Police, Lodge 106.

Violence and resignations have also increased in state prisons, according to William Sullivan, president of a separate union that represents 6,000 New Jersey correction officers, the Police Benevolent Association, Local 105. About 450 officers resign each year, Mr. Sullivan said, and the pipeline for training new guards has slowed drastically.

“You’re seeing a lot more people leave sooner,” he said.

The Essex County jail, a green-sided, low-hung facility, sits in an industrial area of Newark. After years of protests by activists, county leaders decided this spring to stop holding undocumented immigrants awaiting court hearings at the jail, ending a lucrative, yearslong contract with U.S. Immigration and Customs Enforcement.

The lockup has held an average of 2,199 detainees each month over the last year, roughly 240 people fewer than the facility’s legal capacity, county officials said.

Most people in New Jersey’s jails are awaiting trial and presumed innocent, or have been sentenced to terms less than a year. The facilities are run by county administrators, and some have shut down operations as the number of detainees declined after New Jersey effectively eliminated its system of cash bail, enabling most people to wait for their day in court at home, not in jail.

As part of a cost-saving initiative, Union County — where Mr. Boyd lives and where he was charged with two altercations involving family members — has been paying Essex County to hold its detainees since July. (The population of the Union County jail had dropped 67 percent in 10 years, according to the county, and it expects to save $103 million over five years by closing down most of its jail operations.)