The Windsor Police Major Crimes Unit is waiting for autopsy results in a death at the South West Detention Centre.
The post-morten exam is to be performed today on the female inmate.
Officers were called to the jail after 9pm on Sunday.
Correctional staff called 911 and performed first aid until an ambulance arrived. The inmate was transported to hospital where she was pronounced dead.
This is the first death at the facility since it opened in 2014.
The Office of the Chief Coroner and the Ministry of Community Safety and Correctional Services are also investigating.
If the coroner’s investigation determines the inmate's death was not a result of natural causes, a mandatory inquest will be called.