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 film was shot in chronological order.
The production team also built a fifty-foot tall tree for the film.
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.