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).
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.
The goof item below may give away important plot points.
When Ellen takes care of Jake's posterior wound, she remarks that she hasn't worn underwear for ages. However, as she is later tied to a tree by the klansmen and have her clothes torn, she is wearing a pair of large black panties.