Area Fifty-Something is the secret place that serves as the main setting of the whole series. It is run by General Monger. Originally built as a monster prison in order to keep them a secret, its function changed after the Gallaxhar invasion.
- It was introduced in the film and fully named in the pilot episode, Welcome to Area Fifty-Something.
- It is confirmed by the book The Art of Monsters vs. Aliens that Area Fifty-Something is the same facility the monsters where held in before the arrival of Gallaxhar.
- It is revealed in When Nature Shrieks and by looking at General Monger's uniform that the simple way of spelling Area fifty-something is Area 5?.
- To keep secrets, Monger distracts the visitors with a hot air balloon as revealed in The Friend Who Wasn't There.
- There are a number of employees, 2 of which are Janitors, Henry and Doug the night Janitor.
- It has a football field for an occasional bout with The President's secret service.
- In a reference to The Amazing Colossal Man, one soldier was wounded by a giant tranquilizer syringe thrown by Ginormica.
- Besides this military complex, the only other place the staff mingle is the nearby Diner.
- Unlike its real basis, Area 5? is located in South Dakota instead of Nevada.