Factual error: In one of the scenes where Costner is interviewing the witnesses in Dallas. One old guy says he was standing on the overpass and saw a man running back toward the railroad area behind the Grassy Knoll. There is then a shot, back in time, to the day of the assassination, where the shot of the man running is re-enacted. You can see him running by a Ford Mustang. The first Ford Mustangs were not released until April 1964. The man was running by it on November 22, 1963.
Factual error: About two thirds into the film, in a flashback scene, a military-uniformed man is at an airport in New Zealand. In the background the silhouette of a 737-300 is seen landing. The film is set in the early 1960s, but the 737 did not enter service until 1967, and the -300 series not until the mid 1980s.
Factual error: The day of the assassination, Guy Bannister, thrilled with Kennedy's death, sits in a bar with Jack toasting "Camelot in smithereens." The Kennedy administration did not come to be known as Camelot until Jackie Kennedy mentioned her husband's fondness for the musical in interviews several weeks after the assassination.
Factual error: Throughout the movie, it's been said that President John F. Kennedy's motorcade route had been changed at the last minute. This is not true. The route was set in stone for days. In fact, assassin Lee Harvey Oswald supposedly found out that Kennedy was going to ride right past Oswald's work building from a newspaper days before. He rode the same route the newspaper published.