Durham Regional Police say witnesses have indicated that a northbound Toyota Corolla was travelling "at a high rate of speed" on Harwood Avenue when it crossed a centre line and struck an oncoming Nissan Ultima on Sunday afternoon.
The Toyota then struck a hydro pole on the west side of the road.
A driver and two passengers inside the Nissan were taken to a local hospital.
Police say the Toyota driver was extracted from her vehicle and then airlifted to a Toronto-area hospital where she later succumbed to her injuries.
The deceased has not been publicly identified, though police say she was from Ajax.
Police say "speed and driver inexperience" are being investigated as potential factors in this collision.
The collision remains under investigation. Police are asking witnesses to contact investigators at 1-888-579-1520, ext. 5231.
Tips can also be passed on anonymously through Crime Stoppers at 1-800-222-8477.