The inmate, whose name was withheld, was arrested the previous evening by the Tustin Police Department.
"As deputies worked to control the individual he became unconscious," said a statement from the Orange County Sheriff's Department, describing the incident at the Intake Release Center in Santa Ana.
According to the news release, deputies began life-saving efforts and summoned jail medical staff. Orange County Fire Authority paramedics also responded, and the inmate was transported to a hospital.
He was pronounced dead at the medical center around noon, the sheriff's department said. His name was not immediately disclosed, pending notification of his family.
In accordance with protocol, the District Attorney's Office is leading the investigation into the inmate's death and will issue a report detailing its conclusions, the news release said.
Coroner's officials are expected to determine the official cause of death.