The woman, who was hospitalized for a short time, is now recovering at home, Santa Clara County Valley Health and Hospital System spokeswoman Joy Alexiou said.
She is the first human known to be infected with the virus in Santa Clara County since a case in 2011, in which the victim died, Alexiou said.
Other instances of human infection in the county have been relatively rare; there was one case in 2008, four in 2007 and five in 2006, Alexiou said.
Statewide so far this year, 14 people have contracted West Nile virus and two have died from it, Alexiou said.
West Nile virus is transmitted to humans and animals through mosquito bites, but the chance of becoming seriously ill from it is very low, Alexiou said.
Less than 1 percent of people infected develop neurological diseases such as encephalitis, an inflammation of the brain, or meningitis, an infection of the brain and spinal cord, Alexiou said.
The incubation period after a bite from a mosquito carrying the virus is usually two to six days, but can be up to two weeks, Alexiou said.