Visible crew/equipment: In the scene where Brody approaches the group of teenagers on their smashed boats, the angle cuts to show Brody approaching seen as if from Cable Junction. At this point, there is a huge mistake. The teenagers' boats are clearly visible in the foreground, the kids have all completely vanished, and you can spot the cameraman standing on the boats quite clearly.
Continuity mistake: The dressing that is on the evil Dr Leticia Baines's forehead keeps changing. When she is first placed on Grogan's raft, the dressing is soaked with blood. In the next few scenes it just has a small patch of blood in the centre. After she swims to rescue the boy from his canoe, she gets on the raft and the dressing is dry. In the next two close-up shots the dressing is wet (with water) and then it is dry again.
Factual error: The movie takes place in Chicago, except for one scene that is supposed to be in New York City (when Damien's uncle visits the priest). Two problems. First, as the cab pulls up to the church where the priest is, it goes past a housing project. Anyone who knows public housing construction in New York and Chicago knows that building is in Chicago. Second, when they go out to a trainyard, you can clearly see the Hancock Tower in the background. Of course, that building is in Chicago, not New York.