The Klan leader tells Freddie Lee Cobb that if he brings five friends who share similar ideals, they can all be part of the Klan. However, during their introduction to the group, Cobb only brings three guys.
At the airport, when Jake sends his family away, a UPS plane can be seen in the background. At that airport, the cargo terminals are south of the passenger terminals, and cannot be seen from the north side of the terminal (where the outside scene was set).
The movie shows Carl Lee being found not guilty by reason of insanity and ends with him fully free and able to attend the same event as Jake. That is not how that law actually would be carried out. While Carl Lee wouldn't face jail time, he would certainly face either a term of commitment at a mental facility or supervised probation, and would not be able to resume a normal life as quickly as is shown here.
When Ellen and Jake officially meet for the first time outside of Jake's office building, Jake asks Ellen what brings her to Canton. Ellen replies that it was Carl Lee Hailey that brought her to town. But in fact Ellen came to town for the arraignment of the rapist Billy Ray Cobb and James Louis Willard, before she would have known who Carl Lee Hailey was.
When Rufus and his team dramatically enter the courtroom, the inner doors fly open as if they're walking at speed into the room. But the outer doors just behind them are fully closed, indicating they were waiting in that chamber for the "action" cue.