The bird was discovered near Hillcrest Avenue and Yellowstone Drive, district spokeswoman Deborah Bass said.
"With West Nile virus activity in several counties around us, we knew it was just a matter of time," Bass said in a statement.
While most people infected by the mosquito-borne virus don't have symptoms, it can cause symptoms including fever, head and body aches, joint pain, diarrhea or a rash, according to the Centers for Disease Control and Prevention.
This year, the vector control district is also warning residents about the risk of infection by the yellow fever mosquito and the Asian tiger mosquito, both of which were recently found in California.
The public is advised to keep mosquitoes at bay by dumping standing water, wearing mosquito repellent and ensuring window screens are in place.
Residents can report mosquito problems, including reports of water sources where mosquitoes may be developing, to the district at (925) 771-6195.