Interior shots in the Sheriff's office, courtroom, and stairs from the courtroom were filmed in the old Carroll County courthouse in Vaiden, Mississippi. Built in 1905, the building was in such disrepair, that crew and extras had to dodge falling bricks during filming. Though slated for listing in the National Register of Historic Places, the courthouse has been demolished.
At one point, Gene Hackman decided that he would no longer make more violent films, after seeing a brief and violent clip of his performance in this film (and taken out of context, he thought) at the 1989 Oscars. That stance prevented him from accepting a future job as director of The Silence of the Lambs (1991) and almost cost him the Sheriff role in Unforgiven (1992), which he reluctantly accepted after being convinced by Clint Eastwood, a role that earned great acclaim, and his second Oscar.
During the filming of the racists versus reporters scenes on a bridge over the Big Black River near Bovina, Mississippi, two extras were nearly killed by a train when they ventured from a holding area onto a tall concrete-arch railroad bridge. They narrowly escaped injury by huddling on a tiny pedestal on the bridge's edge.
A Klansman in a red car with tall fins and white roof throws a victim out of the door in the town square. The car is a 1961 DeSoto, the very last edition of the historic make. Rumors that the Chrysler Corporation (DeSoto's parent company) decided to drop the line, because of its association with the Klan are untrue. DeSoto's sales had been steadily declining since 1955, and Chrysler decided that the 1961 model would be its last.
Although a fictionalized account of the investigation of the murders of three civil rights workers in the 1960s, the film has been criticized by some for distorting history even as it has won widespread acclaim. However, regardless of whatever liberties the movie did, or didn't take with the facts of 1964 Mississippi, one scene has the absolute ring of truth: the radio roar of a distant crowd cheering a home run by a member of the 1964 St. Louis Cardinals. For all its apparent authenticity, however, including the actual voice of the longtime Cardinals announcer Jack Buck, the baseball broadcast is pure fiction.
The news interview clips were filmed by Alan Parker, with real locals from Mississippi, and their lines were ad-libbed with only minor prompting. Parker said it was at times an uncomfortable experience, since he wasn't always sure if they didn't believe what they were saying.
The trivia item below may give away important plot points.
Alan Parker and his crew whipped up batches of what they called "O.M.D.", or "Old Man's Dick". This ugly mix of purple, yellow, and brown was painted on every piece of set, every chair, every table top, every prop. They made up a dye, and dipped costumes into it, everyone's from the F.B.I. Agents, the white supremacists, and the black civil rights campaigners, who are murdered at the start. Stephen Tobolowsky (Clayton Townley) saw the process first hand, then went to the film's premiere, and wondered why the stuff wasn't showing up on-screen. Parker ambushed him afterwards and asked him, "What did you see?". Tobolowsky said he hadn't seen "O.M.D." Parker replied, "I didn't ask you what you didn't see, I asked you what you saw." Tobolowsky suddenly realized his eyes were drawn to the black actor's skin. "Alan's face turned a lovely red, and he said, 'Right'," Tobolowsky said. The only thing "O.M.D." didn't touch was human skin. You watch the film, and the "O.M.D." is invisible, but it gives everything, except human skin, a dull sameness, that makes your eyes look elsewhere, to human skin, the most important visual in a film about racism.