The movie is dedicated to Lorraine Warren (portrayed in the movie by Vera Farmiga) who passed away two months before the film's release.
(at around 50 mins) The real Annabelle is at the Warrens' Occult Museum in Monroe, Connecticut, kept in a glass case with warning signs. Unlike the doll in the film, it is a Raggedy Ann doll. In one scene, Judy is watching a game show when a couple win a trip to Vegas and a Raggedy Ann doll. This is a nod to the real Annabelle.
The samurai armor that features in the Warren occult museum is based on Japanese mythology's demonic warrior, the Oni, marking along with the Ferryman the second cultural mythology entity appearing.
McKenna Grace replaces Sterling Jerins as Judy Warren. Jerins played Judy in the first two Conjuring films and had outgrown the role by the time production commenced. However, Jerins did play Judy again two years later in "The Conjuring: The Devil Made Me Do It".
Like in The Conjuring 2 (2016), Patrick Wilson does his own singing, as he is an accomplished singer and musical star.