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What to Know About West Nile Virus in Illinois Mosquitoes

Posted on June 22, 2023   |   Updated on September 30, 2025
Sidney Madden

Sidney Madden

A Culex pipien mosquito

A Culex pipien mosquito specimen in the insect collection at the Field Museum shows the type of mosquito that carries the West Nile virus. (E. Jason Wambsgans / Tribune / Getty)

West Nile Virus

Virus-positive mosquitoes have been found in four counties: Cook, LaSalle, Morgan, and St. Clair, according to the Illinois Department of Public Health. While no human cases have been reported yet, Chicago health officials are encouraging residents to take precautions, such as:

  • Use a repellent with DEET, Picaridin, or lemon eucalyptus oil
  • Keep grass and weeds short
  • Opt for light-colored, long-sleeved clothes

+ Check IDPH’s West Nile virus tracker, which is updated Mondays.

Is Chicago a ‘Mosquito’ City?

The news about the virus came after Chicago was named No. 2 on pest control company Orkin’s annual top mosquito cities list, a list the city has topped for the last couple of years.

Why are mosquitoes bad here? Well, mosquitoes are attracted to bodies of water — all types, whether they’re clean, polluted, large or small, according to Orkin. And, uh, we do have that big ol’ lake to the east.

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