Paramedics were called to the scene after someone found the woman, called 911 and started performing CPR.
Attempts by paramedics to resuscitate her at the scene were unsuccessful. The woman was unconscious and she was not breathing.
The woman was transported to hospital.
Police later confirmed that the woman had died. The coroner has been notified.
The Vans Warped Tour is taking place at the Molson Amphitheatre on Sunday afternoon. Dozens of punk and rock bands are playing sets during the all-day show.