This is a good question, as we tend to take this fictionalized work as exact historical truth. Miller himself tells us, to some degree, which elements of The Crucible are true and which he's embellished, changed, or fabricated.
In general terms, he says, he has created each of the primary characters out of what can be surmised from actual court documents, letters, news letters, and any references he was able to find from others' writings. Each of the characters who died in the play suffered the exact fate as recorded in history. These are people who actually existed (I've been to Salem and seen their graves), but not everything in the play is exact history.
Miller tells us, in "A Note on the Historical Accuracy of This Play" (found just before Act I in my copy of the play), what he changed to suit his dramatic purposes.
- More girls than the few in this play were responsible for the "crying-out." Obviously few is better for an audience to keep track of on stage.
- More than two judges presided at the trials, all of equal standing. Here, Miller uses two representative judges, one of whom is the more dominant spokesman for the court.
- The actual Abigail was much younger than Miller's Abigail. That means the whole affair with Proctor is not historically accurate; Miller tells us he gave his audience this motive for Abigail because anything more like what was real would have seemed too unbelievable for modern audiences to accept. We understand why she wants to stir up trouble in the play; in reality, she was probably just trying to keep herself out of trouble for some minor (in our view) transgression. The idea of such severe Puritanical punishments for such minor offenses is just too far removed from today's audience.