London police were at the Elgin-Middlesex Detention Centre on Tuesday after the body of an inmate was discovered in the segregation unit.
Although the exact cause of death is unknown, police say foul play is not suspected.
The force's Forensic Unit was called to the jail to assist the coroner in his investigation.
The inmate, who was admitted to the jail on Sunday, made a court appearance by video earlier Tuesday morning.
He had been on suicide watch, with correctional officers checking on him regularly, and was found unconscious around 10:30 a.m.
Efforts by jail staff to revive him were unsuccessful and he was pronounced dead around 11:30 a.m.
The Elgin-Middlesex Detention Centre was being kept on lockdown while the investigation into the death continues.
Meanwhile the Minister of Community Safety and Correctional Services has released a statement on the death.
In an email, Yasir Naqvi said, "I am saddened to learn of the passing of an inmate at the Elgin Middlesex Detention Centre, and my thoughts and condolences are with the family and loved ones of the deceased. Any time there is a death in any of our facilities it is difficult for all involved."
He added, "The safety and security of correctional staff and inmates is our top priority. A number of thorough investigations will take place, which include a police investigation, the ministry’s internal investigation and a Coroner’s investigation - which will be followed by a coroner’s inquest if the death was not a result of natural causes. It would be inappropriate to comment further on this matter as it is currently under investigation."
