The person who died was identified only as a resident of the San Fernando Valley. They had been hospitalized from a brain illness linked to the virus, according to the county's Department of Public Health.
West Nile is transmitted through the bite of an infected mosquito. Symptoms include fever, muscle aches and tiredness.
There have been 19 confirmed West Nile cases documented in the county so far this year.
Most mosquitoes don't carry the virus but officials reminded people to take precautions against mosquitoes, such as eliminating standing water around your home.
Using repellents containing DEET also protects against mosquitoes.