https://www.wired.com/story/community-spread-coronavirus/

During the press conference where President Trump announced that Vice President Mike Pence would be taking charge of domestic efforts to combat SARS-CoV-2, the new coronavirus spreading internationally, the Centers for Disease Control and Prevention also announced that the outbreak had entered a new phase in the US. The agency reported the first patient infected via “community spread”—which is to say, the patient hadn’t traveled to places where the virus is common and had no known exposure to anyone with Covid-19. WIRED has learned that the patient has been in a northern California hospital for a week, but went undiagnosed until Sunday.

The CDC specified only that the patient was in California; the California Department of Public Health announced that the patient was a resident of Solano County—which, as other reports have pointed out, is the location of one of the Air Force bases being used for quarantines of people who’ve returned to the US from countries with the disease.