The Department of Public Health says a 24-year-old woman from Fontana has been hospitalized with the mosquito-borne illness.
Other Southern California counties where cases were reported were Los Angeles, Ventura and Orange.
Gail Failla of Lancaster said her father is fighting for his life after being diagnosed with the West Nile virus. He is currently in the hospital recovering.
"He lost all motor control, he couldn't move his arms, he couldn't move his legs, he couldn't talk, he actually hallucinated," she said.
Previously, chickens and mosquito samples had tested positive for the virus. West Nile virus activity across the nation this year has been at a record high. So far, there have been more than 1,100 cases reported. There have been at least 26 deaths attributed to the West Nile virus in 2012, according to the Centers for Disease Control and Prevention
Two more West Nile deaths were recently confirmed 2,000 miles apart, in Dallas and Fresno counties. The Fresno death is the second in California. The first West Nile-related death in the state was reported in Kern County.
The illness has touched many states across the nation. There have been five confirmed non-fatal cases across Tennessee so far this year, Arkansas has 10 cases so far and Mississippi has 80 human cases.
The hot, dry weather across the nation's midsection has created ideal conditions for some species of mosquito. The heat speeds up their life cycle, which accelerates the virus replication process. And during a drought, standing water can quickly turn stagnant when it's not flushed away by rain or runoff.
In Southern California, local vector control is urging families to eliminate standing water on their property so the mosquitoes that carry the virus don't have a place to breed.
Several Texas counties have launched a controversial aerial spraying campaign to try to control the mosquito population. The Environmental Protection Agency says the insecticide poses no significant threat to people or animals.
The CDC says this is one of the worst years for infection since West Nile was first detected in the U.S. in 1999.
ABC News contributed to this report.