It was the state's third bird since May to test positive for the mosquito-borne virus. The first was in Henderson County, and the second in Kankakee County.
The virus can be fatal to humans, and can cause fever, headaches or body aches. The elderly or people with weakened immune systems can suffer encephalitis, which can be fatal.
Last Friday, officials reported that four batches of mosquitoes tested positive for the virus, three in Lake County and one in DuPage County.
Illinois led the nation last summer with nearly 900 cases of the virus and 64 deaths. Nationally, 284 people died out of 4,156 cases.