In The Lord of the Rings: The Return of the King, Bilbo celebrates his 111th birthday at the famous party in the Shire.
Bilbo’s birthday party is shown in the opening of The Fellowship of the Ring, although the question’s story spans the film trilogy. The event takes place at Hobbiton and attracts a large gathering of hobbits. Bilbo’s speech includes the memorable remark that he does not know half of the guests as well as he should like, and likes less than half of them half as well as they deserve.
Bilbo uses the party as the occasion to disappear with the help of the One Ring. He leaves the Ring to Frodo, despite Gandalf’s concern about its influence. The number 111 is important because hobbits are known for their long lifespans, and Bilbo’s age makes the celebration especially notable. The party should not be confused with Frodo’s birthday, which is also on September 22 and occurs on the same date in the story.