Around 1 a.m., emergency crews responded to a single vehicle collision in the westbound lanes of the 401.
Officers say the vehicle was travelling in the westbound lanes near Orford Road when it left the roadway and came to a stop in a treeline on the north side of the highway.
Police say a 37-year-old Windsor woman was pronounced dead at the scene.
The westbound lanes were closed for approximately seven hours but have since reopened.
OPP say more information will be provided as it becomes available.