Character mistake: When Lisa is taken to the hospital, she tells Kathy that she saw the ghost of Jodie DeFeo. The name of both of the DeFeo's daughters wasn't Jodie. Their names were Dawn and Allison. Jodie was the name of a demonic pig that the Lutz's daughter Missy had befriended.
Suggested correction: While this is true in the original novel, the writers chose to change it to the DeFeo's daughter's name in the movie. Creative license doesn't count as a mistake.
Factual error: There is a poster for Whitesnake on Billy's wall. This movie takes place in 1975. Whitesnake didn't form until three years later.
Factual error: There is an Alice Cooper poster on the wall of the boy's bedroom. The logo on the poster was not used before the 2000's.