Lake Forest and Lake Bluff residents should take extra precautions against mosquito bites this holiday weekend after the first West Nile virus-positive mosquito pool of 2026 was reported in Lake County on Friday, June 26, according to the Lake & McHenry County Scanner, a local news aggregator citing health officials. The Lake County Health Department has not yet issued a separate public statement on the detection.
The finding comes as the CDC warns that 2026 is shaping up as the worst West Nile season in two decades nationally, and it follows a 2025 season that brought elevated case counts across the region.
Local and regional context
In 2024, Lake County recorded six human West Nile cases, according to Illinois Department of Public Health data cited in a July 2025 Chicago Tribune report. By mid-August 2025, 56 of 337 mosquito batches tested in the county were positive for the virus, and at least one Lake County resident had become ill, according to Emily Young, the Lake County Health Department's marketing and communications manager.
The North Shore Mosquito Abatement District, which serves communities adjacent to Lake Forest and Lake Bluff, detected its first positive pools of 2026 even earlier. Executive Director Mark Clifton confirmed positive samples in Wilmette, Evanston, and Northbrook on Tuesday, June 16, the first out of 217 pools tested in the 2026 season.
"The detections will increase as we move forward in the season," Clifton told the Chicago Tribune. "It's hard to know exactly how many mosquitos are infected, but this is about the time where you start seeing it."
Clifton noted that 2025 brought the district's highest recorded infection rate, with roughly 56 out of every 1,000 mosquitoes testing positive at peak.
National picture
The CDC reported Wednesday, July 1 that at least 48 human West Nile cases had been confirmed across 23 states as of Monday, June 30. That is nearly five times the average of 10 cases typically reported by the end of June since 2004. Of the 48 cases, 38 involved severe neuroinvasive disease affecting the brain or nervous system.
CDC Medical Epidemiologist Dr. Erin Staples urged families celebrating Independence Day to take precautions against bites, saying mosquito season is well underway.
West Nile virus is the leading cause of mosquito-borne disease in the contiguous United States. About one in five infected people develop fever and flu-like symptoms; fewer than 1% develop severe neurological illness. Adults 60 and older and those with weakened immune systems face the greatest risk, according to the Lake County Health Department. There is no vaccine or specific treatment.
How to protect yourself
The Lake County Health Department recommends its "Four Ds of Defense":
- Drain all standing water around your property
- Defend with EPA-approved insect repellent
- Dusk to Dawn — limit outdoor time during peak mosquito-biting hours
- Dress in clothing that covers exposed skin
West Nile activity typically peaks in Lake County from July through September. The health department conducts ongoing mosquito surveillance throughout the season; residents can monitor updates at lakecountyil.gov/health.
