The house seen in the movie in real life doesn't and never actually did exist. The film-makers could not find a suitable mansion to use for the film so at a cost of around $200,000, the production had a Victorian gothic mansion facade attached to the front of a much more modern dwelling in a Vancouver street. This construction was used for the filming of all the exteriors of the movie's Carmichael Mansion. The interiors of the haunted house were an elaborate group of interconnecting sets built inside a film studio in Vancouver.
The real life haunted house where the real life events apparently took place was the Henry Treat Rogers Mansion which was located at 1739 East 13th Avenue, Cheesman Park in Denver, Colorado. The house has since been demolished.
The movie is based on events which supposedly took place at Henry Treat Rogers Mansion in Denver, Colorado, whilst writer Russell Hunter was living there during the 1960s. The Chessman Park neighborhood in the movie is a reference to Cheesman Park in Denver, where the original haunting transpired.
Screenwriters [Diana Maddox] and William Gray spent around six months doing research for the picture which included copious newspaper articles on parapsychological encounters, over seven hundred books and almost two thousand case histories.
The meaning of the movie's "Changeling" title is defined as being, "a creature found in European folklore and folk religion. It is typically described as being the offspring of a fairy, troll, elf or other legendary creature that has been secretly left in the place of a human child. Sometimes the term is also used to refer to the child who was taken". It is the "swapped child" meaning of the term that is of relevance to this film's story.
Spanish filmmaker Alejandro Amenábar has claimed in several interviews that this is one of his all-time favorite Horror movies, up to the point of inspiring several scenes of Thesis (1996) and The Others (2001).
Although Rick Wilkins is the credited film composer, the music box composition is actually written by Howard Blake. The unabridged composition is featured in his Lifecycle collection of 24 piano works in 24 keys.
Director Peter Medak said he was initially intimidated by stories of actor George C. Scott being difficult to work with. The only trouble Medak had with Scott on the set was when production managers accidentally knocked over a chess board on which Scott had been playing a game against himself for over two weeks.
Though predominantly filmed in Canada, the picture was set in Seattle, USA where establishing shots were filmed. These included the Rainier Tower, the SeaTac Airport, the University of Washington's Red Square, and the Lacey V. Murrow Memorial Bridge. Some location filming was shot in New York. Most of the movie was filmed in Vancouver and its environs in British Columbia with Victoria in the same Canadian province also used. Interiors set at the university were shot in Toronto in Canada's province of Ontario.
The name of the history group was the Seattle Historical Preservation Society. The name of the campus where Dr. John Russell (George C. Scott) taught music was the University of Seattle (though the interiors were filmed at the University of Toronto in Toronto, Canada).