2009 (MMIX) was a common year of the Gregorian calendar that started on a Thursday. From July 17 to July 19, The Ultimate SpongeBob SpongeBash, a 50-hour nonstop marathon, was airing. It celebrated the 10th anniversary of the series. 32 episodes premiered this year. This is the same amount of episodes that aired the previous year as well. A second TV movie, "Truth or Square," premiered in November.
- February 16: Shuffleboarding and Slide Whistle Stooges premiered.
- February 17: Cephalopod Lodge premiered.
- February 18: Grandpappy the Pirate premiered.
- February 19: Professor Squidward premiered.
- February 24: SpongeBob's Greatest Hits was originally released.
- March 16: Sand Castles in the Sand premiered.
- March 17: Toy Store of Doom premiered.
- March 18: Pet or Pests premiered.
- March 19: Komputer Overload premiered.
- March 20: Choir Boys premiered.
- April 17: SpongeBob SquarePants vs. The Big One premiered.
- May 1: The SpongeBob SquarePants Series became 10 years old.
- June 1: Shell Shocked premiered.
- June 2: Pineapple Fever premiered.
- June 3: Single Cell Anniversary premiered.
- June 4: Squid's Visit premiered.
- June 5: Gullible Pants premiered.
- July 14:
- July 17: The Ultimate SpongeBob SpongeBash begins with To SquarePants or Not to SquarePants.
- July 18: Chum Caverns premiered.
- July 19: Goo Goo Gas (along with a re-air of Le Big Switch), No Hat for Pat, Someone's in the Kitchen with Sandy, Chum Bucket Supreme, Growth Spout, Tentacle-Vision, The Inside Job, Stuck in the Wringer, and to finish the SpongeBash, Overbooked premiered.
- August 15: The SpongeBob Community Forums was founded.
- October 24: The Curse of Bikini Bottom premiered.
- November 6: Truth or Square premiered, before Fanboy and ChumChum.
- November 27: Greasy Buffoons and Model Sponge premiered.
Home media (North American DVD releases only)
- January 27 - Spongicus was released.
- March 3 - SpongeBob vs. The Big One was released.
- April 7 - 10 Happiest Moments was released.
- July 21 - To SquarePants or Not To SquarePants was released.
- November 10 - Truth or Square was released.