Sidney Poitier insisted that the movie be filmed in the north because an incident in which he and Harry Belafonte were almost killed by Ku Klux Klansman during a visit to Mississippi. Hence the selection of Sparta, Illinois for the location filming. Nevertheless, the filmmakers and actors did venture briefly into Tennessee for the outdoor scenes at the cotton plantation, because there was no similar cotton plantation in Illinois that could be used. Poitier slept with a gun under his pillow during production in Tennessee. Poitier did receive threats from local racist thugs so the shoot was cut short and production returned to Illinois.

This was the first major Hollywood film in color that was lit with proper consideration for an actor with dark skin. Haskell Wexler recognized that standard lighting used in filming produced too much glare on most black actors and others of dark complexion. Wexler toned down the lighting to feature Sidney Poitier with better results.

Rod Steiger was asked by director Norman Jewison to chew gum when playing the part. He resisted at first but then grew to love the idea, and eventually went through 263 packs of gum during the shooting of the film.

Set in a hot Mississippi summer but filmed during autumn in Illinois, many of the actors had to keep ice chips in their mouths (and spit them out before takes) to prevent their breath from appearing on camera during the night scenes.

The movie's line "They call me Mister Tibbs!" was voted as the #16 movie quote by the American Film Institute

According to Sidney Poitier, Tibbs' retaliation slap to Endicott was not in the original script nor in the novel on which the film is based. Poitier insisted that Tibbs slap Endicott back and wanted a guarantee that the scene would appear in all prints of the film. According to Stirling Silliphant, the slap was in the original script though not in the novel.

When Norman Jewison and his editor Hal Ashby attended a sneak preview for the film, they found that the young audience was laughing uproariously at the dialogue. Although Jewison was upset that his dramatic film was not being taken seriously, Ashby assured him that the audience was laughing in approval of the southern sheriff being put in his place by the confident and urbane Det. Virgil Tibbs. Jewison did not agree until the film got to the famous slapping scene; when the white audience was stunned at seeing an African American man physically fight back against a white man for the first time in a modern mainstream American film, Jewison was convinced the film was effective as drama.

The scene that took place at the sheriff's house featured dialog that came out of improvisations between Sidney Poitier and Rod Steiger.

Producer Walter Mirisch used creative accounting to prove to United Artists that the film would make a profit even if it did not play in the South at all.

Frequently cited as Sidney Poitier's favorite of all the films he's done.

Mississippi was eventually ruled out as a location due to the existing political conditions. Sparta, Illinois, was selected as the location, and the town's name in the story was changed to Sparta so that local signs would not need to be changed. The greenhouse was added to an existing home and filled with $15,000 worth of orchids.

Due to the assassination of civil rights activist Martin Luther King (April 4, 1968), the presentation of the Best Picture Oscar for this film was postponed for two days from Monday April 8th to Wednesday April 10, 1968. (see also - The Life of Emile Zola (1937) and Raging Bull (1980)).

According to Norman Jewison and Haskell Wexler on the DVD commentary, they originally wanted to use "Lil' Red Ridin' Hood" by Sam the Sham and The Pharaohs in the movie, and this is the song Ralph Henshaw (Anthony James) was dancing to during filming. Unable to license Sam the Sham's song, "Foul Owl on the Prowl" was substituted, composed by Quincy Jones and performed by Boomer & Travis (better known as Owens Boomer Castleman and Michael Martin Murphey).

In 2007, the American Film Institute ranked this as the #75 Greatest Movie of All Time. It was the first inclusion of this film on the list.

The slapping scene between Det. Tibbs and Endicott was shot in just two takes, and the slaps the characters made to each other's faces were real, according to a detailed account Norman Jewison, provided in 2011. Jewison let Larry Gates rehearse by slapping him because Jewison wanted to be sure that Gates could slap hard enough.

Rod Steiger received directions to base his performance as Sheriff Bill Gillespie on The Dodge Sheriff, a popular cultural icon and corporate spokesperson for Dodge automobiles. The Dodge Sheriff was a stereotypical southern sheriff used in an array of advertisements in the 1960s. Steiger took the advice, although he greatly toned down the comedic aspects of the character.

Virgil Tibbs was ranked Hero #19 in the Heroes category on the AFI's 100 Heroes and Villains list.

Rod Steiger spoke in the southern dialect consistently for the duration of filming.

Beah Richards, the actress who plays the abortionist Mama Caleba, played the mother of a Sidney Poitier character the same year in Guess Who's Coming to Dinner (1967).

Scott Wilson so impressed Sidney Poitier that he contacted director Richard Brooks and suggested Wilson for a leading role in In Cold Blood (1967). Poitier never mentioned this to Wilson at the time, who only found out about this recommendation after he had been cast.

The movie's line "They call me Mister Tibbs!" was voted as the #76 of "The 100 Greatest Movie Lines" by Premiere in 2007.

Banned by the South African Publications Control Board, as were many of Sidney Poitier's films.

Virgil's salary of "$162.39 per week" would be roughly $1200 in 2017.

George C. Scott was the first choice to play Chief Gillespie but he was unavailable due to The Flim-Flam Man (1967).

The brawl in the maintenance shed takes place under a sign that reads, "Let us ALL be Alert. We don't want ANYONE Hurt."

The same locomotive is used in the opening and closing scenes to carry Virgil in and out of town - Gulf Mobile and Ohio locomotive #103.

In an one on one interview that aired on TCM, Rod Steiger praised Lee Grant for her performance in the film, calling it one of his favorites.

Favorite film of actor Danny Glover.

The bridge the fugitive (Harvey Oberst) runs across while being chased is the Chester Bridge, in Chester, IL, spanning the Mississippi River and over into Missouri.

Lawrence Tierney was considered for the role of Chief Gillespie.

Included among the "1001 Movies You Must See Before You Die", edited by Steven Schneider.

Ironically, Warren Oates and Lee Grant were among Hollywood's group of actors who played racist roles, or were in racist films, but were themselves up front and vocal in support of the civil rights movement at the same time. Others include Shelley Winters, and William Shatner.

The "N-word" is used a total of seven times - all directed at Virgil Tibbs.

The film is considered to be the first part in a loose trilogy of films directed by Norman Jewison that deals with racism, the other two are A Soldier's Story (1984) and The Hurricane (1999).

A sign at the Sparta depot refers to the "Rebel Road." This is a reference to the Gulf Coast Rebel, a named train that began in 1937 and ran between Mobile and Union, MS, and was later extended to St. Louis. However, this would be an out of date artifact in 1966 as the GM&O ceased operations South of St. Louis in 1960 (although the company headquarters were in Mobile until 1972.)

The distributors hesitated to release the movie in the South states because of the high risks related of racial elements it contained. But it eventually occurred that there was no demonstration against the film in those southern states.

Included among the American Film Institute's 1998 list of the 400 movies nominated for the Top 100 Greatest American Movies.

EMD E7A #103, the locomotive featured at the beginning and end of the film, was originally purchased by the Alton RR and acquired by GM&O in 1947 when it bought out Alton. The producers rented the train and crew for the movie.

The only Best Picture Oscar nominee that year to be also nominated for Best Sound Effects.

The only film directed by Norman Jewison to win Best Picture at the Academy Awards.