As of the 2013-2014 season, 24
22
There have been 19 Treehouse of Horror Specials.
The tree houses of horror, are Halloween themed stories that the simpsons do. They have short stories, so in 30 minutes ( the time of a normal episode) there are 3 stories. Most channels play them during Halloween, to get people in the mood. there are many tree houses of horror, and they are great! The Treehouse of Horror 1 was in the 2nd season, so to find what season each ToH was in, just add 1 to the number of the episode.
There are currently twenty-three Treehouse of Horror episodes. There will be a twenty-fourth one for the upcoming twenty-fifth season.
234 episodes aired during that decade.
As of June 2015, 25 seasons have aired.
Bart Gets Hit By a Car, Stark Raving Dad, Treehouse of Horror III, Sideshow Bob Roberts, And Maggie Makes Three, Round Springfield & Lisa's Sax
At the end of 2012, 516 episodes had aired.
The Simpsons episode Treehouse of Horror XIV (which aired in November 2003 during Family Guy's cancellation) features a story entitled "Reaper Madness" in which Homer takes over the duties of being the Grim Reaper. Many Family Guy fans have claimed that it's hypocritical to suggest that Family Guy steals from the Simpsons when the story to this Simpsons episode is very similar to the Family Guy episode entitled "Death is a Bitch" in which Peter assumes the role of death. However, others point out that the story of a mortal taking on the duties of the Grim Reaper has been used several times before "Family Guy" or "The Simpsons". So in short, Family was first! (for once) Chris
429 at the start of 2009449 by the end of 2009
As of November 2014, that would be 22.
there was no episode that has any real crossovers but on October 25, 1998 (a year before futurama premiered ) in the credits for the Treehouse of Horror 5 David Cohen name read David "Watch Futurama" Cohen since then there has been many references have been made to each other