The real Perron family visited the set of the film.
The film was given an R rating by the MPAA for "sequences of disturbing violence and terror". 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 production team also built a fifty-foot tall tree for the film.
The film was shot in chronological order.
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.