Vancouver police announced that Monteith checked into the Farimount Pacific Rim hotel on July 6, and was found by hotel staff at noon on Saturday when he missed his checkout time.
Police did not give a cause of death, but do not suspect foul play.
In March, Monteith voluntarily checked himself into rehab for substance abuse.
Monteith was frank about his struggles with substance abuse, telling Parade magazine in 2011 that he began using drugs at 13, and by 19 went into rehab after his mother and friends intervened.
Monteith played Finn Hudson on Glee since it debuted in 2009.