While in makeup Kevin Peter Hall's already immense height (7'2) was increased to over eight feet. This is evidenced by John Lithgow (who stands at 6'4") when he stands next to Hall
Special makeup effects artist Rick Baker says that Harry is his greatest and favorite character that he created.
The filmmakers kept Harry a secret prior to the film's release - only glimpses of him were shown on all publicity materials and theatrical trailers. Although a wise decision for the film, this was also blamed for the film not being more successful than it actually was due to it not selling the fact that a Bigfoot was the star of the film. As a result, the film was renamed 'Bigfoot & the Hendersons' in many overseas territories, and much of the artwork now featured Harry also. The film however has reverted back to it's original title in the DVD and Blu ray age.
Apart from the opening camping trip and the climatic escape at the end, Melinda Dillon is barefoot throughout the film.
According to Rick Baker, he based the design of Harry off of orangutans, particularly Harry's beard.
According to cryptozoologist Loren Coleman, some characters in the film are based to varying degrees on actual figures in the search for Sasquatch. "Jacques LaFleur" (David Suchet) is a nod to the late Canadian Rene Dahinden, and "Dr. Wallace Wrightwood" (Don Ameche) combines some qualities of John Green, Peter Byrne and the late Dr. Grover Krantz.
M. Emmet Walsh plays John Lithgow's father, when in actuality Walsh is only 10 years older than Lithgow.
Bill Martin, who co-wrote the screenplay, wrote songs for Harry Nilsson's "Harry" album and is pictured (wearing a bear suit) inside the album's cover. Martin says that the character "Harry" in the film is named after Harry Nilsson.
The drawing of Harry that appeared in the film was the original design of Harry done by Rick Baker.
Some deleted scenes include - a scene of Nancy not wanting Harry to go into her kitchen realm on their first night together; George and Nancy laying awake at night worrying for Harry's well being after his escape; Dr. Wrightwood turning up in the neighborhood during the mass media frenzy to ridicule Jacques for his ongoing obsession.
Jacques LaFleurs rifle is a Steyr-Mannlicher SSG PII with double-set triggers (interestingly the rifle goes from having a standard 5-round magazine to a 10-round box magazine in the final scene of the film when LaFleur is hunting Harry in the woods.), he also carries a stainless "4 inch Colt Python.
Regarding the exit the Hendersons take from the freeway. This is the Lake City Way exit from the northbound express lanes of Interstate 5. The DOT highway crews changed the sign from "Lake City Way" to "Mt Rainier". If they simply continue on Lake City Way through Bothell, they will eventually hit Highway 2 which goes up Stevens Pass and into the Cascade Mountains. But they would still be a long way from Mt Rainier.
After Harry sees George on the News Reports, as the police car crashes into the television shop, a Vince and Larry (the Crash Dummies) commercial plays.
Richard Foley and Dana Middleton, the two news anchors listed in the credits, were real-life news anchors and talk-show co-hosts at Seattle's KOMO TV. Their brief appearance in the movie was from the set of their nightly local news magazine "Weeknight" which aired from 1983 to 1985, when it was replaced by the syndicated version of Jeopardy! (1984) when it moved from KIRO TV to KOMO TV. Another reporter is seen in the movie reporting from the actual newsroom of KOMO 4 News. Middleton and Foley also hosted "Northwest Afternoon," an afternoon daily talk show. Middleton left KOMO TV in 1993, and Foley followed suit in 1995.
The Hendersons' station wagon suffers heavy front-end damage including the eventual loss of the front bumper and driver-side headlamps, roof damage from Harry's head, the loss of the rear driver-side door and significant paint scraping down both sides after being run along the center divider on the freeway. Finally the wagon is stolen by Jacques. This is markedly similar, whether intentionally or unintentionally, to the damage inflicted upon Sergeant Murtaugh's station wagon in Lethal Weapon 2 (1989) - it suffers heavy front-end damage including the loss of front bumper and passenger-side headlamps, the rear driver-side door is knocked off, the roof is damaged (by flying toilet), both sides are scraped along a bridge railing, and the vehicle is finally stolen. The only difference is that the windshield is also shot out on Murtaugh's wagon.
The scene when George (John Lithgow) sees Harry approach the deer head on the wall, and exclaims "oh dear!" had multiple meanings; one being that the director of the movie is named William Dear.