The real Perron family visited the set of the film.
The film was shot in chronological order.
The film was given an R rating by the MPAA. The filmmakers had thought the final cut had a chance of getting the more-box office friendly PG-13 rating, and asked the ratings board for clarification. The MPAA said simply that the film was so scary that there were no cuts or edits possible that would make it a viable PG-13 film; the filmmakers did not want to alter the film's tone and accepted the R rating without any appeals.
The film contains no sex or nudity, little profanity, tame and mostly bloodless violence, and brief depictions of alcohol and no smoking, yet it received an R rating. This was solely for its scare factor alone.
Patrick Wilson and Vera Farmiga both traveled to Connecticut to meet with Lorraine Warren prior to filming.
Lorraine Warren: (at around 44 mins) Elder woman in the front row of the classroom when Carolyn is listening to the Warrens' presentation.