The new Tuolumne County case of COVID-19 is a 56-year-old woman who has not traveled outside the county.
The woman has had multiple contacts with people outside her household, the agency said. Some of the contacts have traveled outside the county.
The health department said they have not identified the source of infection, but have reached everyone the woman was in contact with and they are in quarantine.
Michelle Jachetta, the health department health program supervisor, said the agency could not say how many people the patient was in contact with or whether every one of them was tested.
The woman was tested at Adventist Health Sonora and San Joaquin Public Health lab verified the positive result.
She was not hospitalized and is isolated at home.
This is Tuolumne County's third case and the only one in which the person had not gone outside the county. The first two people have recovered.
As of Saturday 890 people in Tuolumne County have been tested.
This story has been edited to reflect that the patient had been in public but had not been in close contact with others.