Officers were called to the scene on Wellington Road 12 Sunday night around 11:50 pm.
Initial reports indicated that a black sedan had left the roadway and the three occupants of the vehicle were injured.
Emergency services responded and all occupants were taken to local hospital.
A 17-year-old driver of Mount Forest was pronounced deceased.
A 15-year old passenger from Mount Forest and a 15-year-old passenger from Southgate were both air-lifted to a trauma centre with serious injuries.
The cause is being investigated and the Wellington County OPP is asking anyone with info related to collision to contact police or anonymously to Crime Stoppers.