Jon Gerald Moore, 44, of Santa Rosa, was serving a sentence for a misdemeanor drug charge in the jail north of Santa Rosa that houses inmates charged with or convicted of lesser offenses.
He was not breathing when a correctional deputy tried to wake him up for his work shift in the kitchen, Lt. Chris Spallino said.
The deputy called for medical assistance and deputies tried to revive Moore before paramedics arrived, Spallino said. Moore was pronounced dead at Kaiser Hospital, Spallino said.
The Sonoma County coroner's office said he was pronounced dead at 2:16 a.m. and an autopsy is scheduled for Monday.
There were no obvious signs of trauma and no evidence of foul play and the cause of death is pending autopsy results, Spallino said.
The death is being investigated by the sheriff's department's violent crimes unit.