In late June, the Will County Health Department announced that a batch of mosquitoes in the city of Joliet, which is around 40 miles southwest of Chicago, tested positive for West Nile virus.

An individual from southern Illinois was hospitalized due to complications from West Nile virus, the Illinois Department of Public Health reported June 24. That case marked the state’s first human case in 2025 and represented the earliest onset of the disease in Illinois since 2016.