Starting Monday, face coverings will be required at San Mateo County facilities, the county announced Thursday.
The requirement is out of an abundance of caution, due to a "troubling rise in coronavirus cases," county officials said in a news release.
Visitors and county employees will need to wear face coverings at county offices, clinics or other public facilities, regardless of vaccination status.
County officials also expressed concerns about the rise of the delta variant of the coronavirus, which is more contagious and spreads more easily.
As of Thursday, the delta variant makes up 83 percent of positive COVID-19 cases that have been sequenced in California, making it the dominant strain in the state.
Last Friday, health officials around the Bay Area recommended that everyone wear masks indoors, regardless of vaccination status.
County Manager Mike Callagy encouraged people to get vaccinated and take common-sense precautions to keep everyone safe.
"The increasing case numbers are a harsh reminder that we are not done with COVID and COVID is not done with us," Callagy said.
Board of Supervisors president David Canepa also supported the mask mandate for county facilities, saying, "No one wants to ditch these damn masks more than I do but we can't do it until we are all vaccinated."
While vaccinations are highly effective against COVID-19 and its variants, county officials said they "need to take action now to protect younger children and overall public health as cases rise."
On July 15, San Mateo County Health recorded 74 new COVID-19 cases, compared to 13 new cases recorded on June 15, the day the state reopened. Hospitalizations have also risen in the last week, with 20 confirmed COVID-19 patients hospitalized as of Wednesday.
A vaccine clinic calendar for San Mateo County is available online. Appointments are not required.