A Cook County man who was in his 60s and had other health conditions died earlier this month.
Eight human cases of West Nile Virus have been reported in Illinois this summer.
The virus is transmitted by mosquitoes that pick up the virus after feeding on infected birds.
Though temperatures are cooler, the danger has not passed.
Crews were out spraying in Wheaton Tuesday night where mosquitoes carrying the virus were discovered in traps.