The latest death happened on Friday when a 51-year-old woman died in the jail's medical unit, according to the Snohomish County sheriff's office.
The woman, who has not been identified, had been housed in the medical unit since being booked last Wednesday. It's unclear what her ailment was, but the sheriff's office says corrections staff had been checking on her at least every hour during her stay in jail.
When they checked up on her Friday night at about 10:30 p.m., the woman wasn't breathing. Staff members called paramedics and immediately began CPR, but the woman was pronounced dead at the scene.
Snohomish County major crimes detectives are now investigating the death, which officials say is standard procedure.
Friday's death was the eighth at the facility since 2010.
William Williams, 59, died in jail last September after jail staff Tased and put him in an isolation cell.
In January, the Snohomish County Medical Examiner ruled the death was homicide.
Williams had been arrested that same night on suspicion of theft for allegedly shoplifting from an Everett gas station. After the death, Aaron Snell with Everett Police said Williams had become combative and wouldn't follow jail staff's commands after he was processed into jail, which led to the physical altercation.
The family of another woman who died in the Snohomish County Jail recently filed a $10 million wrongful death claim.
The claim says complacency by guards and medical staff resulted in the November 2011 death of 27-year-old Lyndsey Elizabeth Lason, who had been arrested for investigation of theft and prostitution.
Michael Saffioti, 22, died in a Snohomish County Jail cell in July of what his mother believes was a severe allergic reaction.
Despite witness testimony that jail guards mocked the dying man, the Sheriff's Office announced earlier this year it would not recommend charges against the guards or staff.