The studio tried to recreate the success of Twilight (2008) with this film by marketing it as a "Twilight for boys". Although it hoped to be a box office success, the movie did not earn the hundreds of millions that the Twilight films grossed.
The evil aliens in the film are called "Mogadorians" - apparently they're from the planet Mogadore. Mogadore also happens to be a small suburb of Akron, Ohio - not far from where the film takes place, and not far from where James Frey, one of the writers of the novel on which this film was based, grew up. The word means "beautiful" in Arabic; it's also the name of a town in Morocco.
Dianna Agron landed her role after a chance meeting with executive producer Steven Spielberg at a charity event. As a big fan of Glee (2009), Spielberg was seriously considering Agron for a prominent part when the chance encounter proved beneficial for both parties.
Just like the aliens are from Mogadore, which is their planet, but also a play on the small Ohio town of the same name, the planet which John and Number Six are from, Lorien (pronounced LORE-EE-en), is a play on the small Ohio town of Lorain (pronounced LORE-rain), which is about one hour northwest of Akron.
The movie is based on a young adult science fiction novel by Pittacus Lore and the first book in the Lorien Legacies series - I Am Number Four, The Power of Six, The Rise of Nine, The Fall of Five and The Revenge of Seven
As stated in goofs, the sheriff uniforms are incorrect, but on top of that, the USA flag on their jackets shoulder faces the wrong way. The stripes point towards the front, but the right way to wear a flag on a sleeve is to orient stripes to the rear of uniform. The reason being that no matter what side it is on, it always looks to be blowing in the wind as if the soldier is running.
The trivia items below may give away important plot points.
Several of the ending plot points were setups for a potential sequel, including coming back to Sarah in Paradise, Sam being "one of us now," the search for Sam's real father, what's in the box, and more.
Right before he dies, Henri (Timothy Olyphant) tells Number Four "You have no idea what you are capable of". Timothy Olyphant uses almost the exact same line in Live Free or Die Hard (2007) when he tells John McClain "You have no idea what I am capable of".