The Wisconsin Department of Health Services says the case was confirmed in a Dane County resident.
Health officials are advising Wisconsin residents to continue protecting themselves against mosquito bites.
The department says the majority of human West Nile cases in the state happen in August and September.
West Nile virus is spread to people through the bite of an infected mosquito and is not transmitted person to person.
The state documented its first human infections from West Nile in 2002. Last year, 51 cases of West Nile infection were reported among Wisconsin residents.