Tijuana, Mexico it seems.
The location of The Hangover III, had been a secret, however an industry insider recently revealed to Life & Style Weekly magazine: "A lot of it will be shot in Los Angeles, but then they are going to do the crazy scenes in Las Vegas again and then one wild week in Tijuana."
The first flick, filmed in Las Vegas and released in summer 2009, earned an incredible $467 million at the box office. Two years later, the second film, set in Bangkok, made even more: $581 million.
The plot of the third film is still under wraps, but Zach Galifiankis recently told Rolling Stone that he heard the plot ditches the format of the first two and focuses on his character escaping from a mental institution with help from the wolf pack.