According to director James DeMonaco, the famous road-rage incident awakening the idea for The Purge happened like this: He and his wife were driving on the freeway when a drunk driver cut them off nearly killing them. After both cars stopped, the other driver's lack of remorse enraged DeMonaco enough to engage in a fistfight and police eventually had to get involved. After the incident was over, DeMonaco's wife turned to him and commented how great it would be to have one free murder a year. He felt bad admitting this because she's normally a "sweet woman".
Director James DeMonaco was asked why the film began with footage of multiple purges taking place outdoors - yet he opted to have all purging occur inside one family's home. He responded, "we only had 19 days to shoot and $2.7 million to work with". If he ever got a chance to do a second one, he vowed it would be more like Escape from New York (1981).
Ethan Hawke is an old friend of producer Jason Blum and director James DeMonaco, and was happy to appear in The Purge to give their low-budget movie some star-power. As usual in Blum's productions, cast and crew work for scale and receive a percentage of the profits, if any. Hawke reportedly received only $3000 upfront, but due to the movie's worldwide success and the back-end profits, he has probably received more money for this film than for any other in his career.
On the prospect of a real Purge, director James DeMonaco once said "...honestly I'd probably just go to Canada and hide."
The homicidal ladies in white dresses were based on Charles Manson's killer/followers. Director James DeMonaco claims obsession with Manson from an early age.