The region's medical officer of health says an adult woman from Kitchener tested positive for a mild form of the mosquito-borne virus.
Dr. Liana Nolan says the woman is recovering.
There are currently 19 probable and human cases of West Nile virus across the province.
Health officials say people should limit their time outdoors between dusk and dawn and wear a mosquito repellent with DEET in it.
Most people who get West Nile will have symptoms such as a fever, headache, body ache, nausea, vomiting and a rash on their chest, stomach or back.
But about one in 150 people infected will have more serious symptoms including high fever, severe headache, muscle weakness, stiff neck, confusion, tremors, numbness and sudden sensitivity to light. (CKGL)