Dr. Mark Clifton of North Shore Mosquito Abatement District sat down with ABC7 Chicago and said his team found the infected mosquitoes last week in Evanston, Glencoe, Glenview, Northbrook, and Winnetka.
"When you see a lot of virus in mosquitoes it is an indication that human illness is close behind, but we are not there yet," said Dr. Clifton.
Each one of the mosquitoes were analyzed at their lab.
RELATED: 4 plants you need to keep mosquitoes away
"We can actually isolate the DNA of the virus and test for it," said Dr. Clifton.
This marks Cook County's first round of West Nile positive mosquitoes this year. Officials said the testing is normal this time of year.
"If we know what the levels of the virus are in the mosquitoes, we can act to prevent human illness," stated Dr. Clifton.
In 2018 the Illinois Department of Public Health reported 176 human cases of West Nile virus, 17 of which were fatal.
Currently, there are no confirmed cases of humans contracting the virus, which is spread through mosquito bites.
"It is too early to tell - you just have to test the mosquitoes as they come in to know what is happening," said Dr. Clifton. "It has not been that warm, and bad years depend on a really hot season."
Mosquito abatement teams are reminding everyone to check their yards for areas of standing water because if it can hold water, mosquitoes can breed.
"It is too early to tell [but] things could turn hot anytime and change," said Dr. Clifton.
Experts also suggest using mosquito repellent to protect yourself.
The health department says the primary mosquito that spreads West Nile virus prefers hot and dry weather, while nuisance mosquitoes enjoy wet weather - which is what people are seeing right now.