The cause of the Sunday uprising, which was brought under control in about 9 hours, was not known, CNN reported Monday.
"The disturbance is contained within the secure perimeter of the facility, with no threat to public safety," said a statement from the operator of the Adams County Correctional Facility.
The guard, 23, died of head injuries, the county coroner said.
Five employees and one inmate were taken to a hospital. Other staff members were treated at the 2,567-bed prison.
Adams County Sheriff Chuck Mayfield said inmates used anything they could find as weapons, the Natchez Democrat reported.
"There were around 300 inmates [participating], so there's no way to tell if it was organized," Mayfield said.
Mayfield said reports of escaped convicts were false.
"I just want people to understand, and know, that no one has gotten out and no one will," Mayfield said.
The Tennessee-based Corrections Corporation of America owns the Natchez facility, a prison for adult men in the United States illegally and charged with crimes.