The cast, crew and network executives behind the hit Tv series gathered on the show's set in California to mark the occasion.
Dana Walden, chairman of 20th Century Fox Television, gave a moving speech at the event and paid tribute to Monteith, who died of a drug overdose last year (13).
Walden said, "We've celebrated so many milestones on this stage and most recently we celebrated the life of our good friend and colleague, Cory Monteith. I miss Cory a lot today. He was always front and center at an event like this; he really loved them and was always smiling in the front row. He was so proud of this show. He was blown away by the talent that surrounded him - and he had very good reason to be proud."
Former cast members Dianna Agron and Amber Riley returned to film appearances in the milestone 100th episode alongside Lea Michele, Chris Colfer, Darren Criss, Naya Rivera.
The show's two-part 100th episode is set to air in the U.S. on 18 March (14) and 25 March (14).