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. 12 episodes premiered this year. A second TV movie, Truth or Square, premiered in November.
32 episodes premiered this year. This is the same amount of episodes that aired the previous year as well.
- February 16 - Shuffleboarding and Slide Whistle Stooges premiered.
- February 17 - Cephalopod Lodge premiered.
- February 18 - Grandpappy the Pirate premiered.
- February 19 - Professor Squidward premiered
- 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 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, I ♥ Dancing, Tentacle-Vision, Growth Spout, Stuck in the Wringer, Someone's in the Kitchen with Sandy, The Inside Job, Chum Bucket Supreme and to finish off the SpongeBash, Overbooked premiered!
- October 24 - The Curse of Bikini Bottom premiered
- November 6 - Truth or Square premiered
- November 27 - Greasy Buffoons and Model Sponge premiered.