I'm sure you've seen the movie, or maybe even read the book. 

In my vague recollection of the movie (never did read the book) the one who is possessed is a little girl, and her mother is a famous actress. Lots of stuff happens, and they end up getting a lot of pea soup everywhere and eventually a priest jumps out of their window.

The book was written by William Peter Blatty.  He did some research about supposed exorcisms and came across one, that he loosely based the book around.  However, the actual case and the book vary, because, you know, creativity.  The real case was of a boy called Roland or Robbie (to protect his identity, fake names, you know) who was about 14 years old.  It started not after an encounter with a Ouija board, but after his aunt died - even though she was close to him and they did play with a Ouija at some point.

The story started in Georgetown, like it does in the movie, and they tried to do something there, but for the big time exorcism part, the family traveled to St Louis.  Namely to a relative's house on Roanoke Drive in St Louis.  That's where Father William S. Bowdern, a catholic priest, comes in. The priest took him to The Alexian Brothers Hospital (not there anymore, burned down), and that's where it all went down, not somebody's house. He had the help of Raymond J. Bishop, Walter Halloran and William Van Roo - so it was a lot more dudes involved than the movie (a lot of Williams in this story, as well.  Coincidence?!). And, it doesn't look like anyone died taking care of this boy, so there's that as well.

The actual scary stuff is probably just as bad as you saw in the movie.

During the exorcism, the boy allegedly slipped one of his hands out of the restraints, broke a bedspring from under the mattress, and used it as an impromptu weapon, slashing the priest's arm and resulting in the exorcism ritual being halted....they allegedly observed a shaking bed, flying objects, the boy speaking in a guttural voice, and exhibiting an aversion to anything sacred...words such as "evil" and "hell", along with other various marks, appeared on the teenager's body... Allegedly, during the Litany of the Saints portion of the exorcism ritual, the boy's mattress began to shake. Moreover, Roland broke Halloran's nose during the process.

I got that all from Wikipedia, so... you might have to take someone's word on that. Apparently after a lot of tussling and probably a lot of chanting and screaming, the kid was perfectly fine, just like the little girl in the movie. And it all took place right here in Missouri.   Kinda spooky, but I gotta admit... I'm skeptical.  It could have been just a huge ploy for attention or mental illness.  I guess we'll never know - but now we know where it happened!

Spookily yours,

Behka