The Vancouver police gave no details about the cause of death and an autopsy will be conducted Monday.
The star had been residing at the Fairmont Pacific Rim hotel in Vancouver, Canada, from July 6.
When he missed his checkout time, the hotel staff found him dead.
The tragic news was confirmed by the police in a press conference.
“We are so saddened to confirm that the reports on the death of Cory Monteith are accurate,” Cory Monteith’s rep said in a statement. “We are in shock and mourning this tragic loss.”
His colleagues on the show have reacted to the actor’s death by posting messages on social networks.
In March Cory Monteith checked himself to rehab to treat his addiction to substances and was released in April.
“Sending out big love to everyone. thank you for the continued support! It means the world to me! :), the actor tweeted after he left rehab.
Cory Monteith spoke out about drug abuse in 2011, saying he started using drugs at 13, and by age 19 he was already hospitalized for rehabilitation.
Speaking about his past, Monteith revealed: “[I used] anything and everything, as much as possible. I had a serious problem. I’m lucky to be alive.”
At the time he checked into rehab, his girlfriend Lea Michele told People when he was decided to enter rehab: “I love and support Cory and will stand by him through this.”
“I am grateful and proud he made this decision,” she added.
Cory Monteith starred in the musical comedy “Glee” when it debuted in 2009.