Act One -- and the entirety of the play -- is set in Salem Village in the Massachusetts Bay Colony, which was settled by Governor John Winthrop and around seven hundred Puritans in 1639. Though the play takes place in 1692, the year in which the historic and infamous Salem Witch Trials began, this Puritan community would be largely unchanged. They left England because they did not feel that the Church of England had done enough to distance itself from the Catholic church (which they viewed as incredibly corrupt); they felt that they had a responsibility to guide the rest of the world out of spiritual darkness, to be a model for the perfect community in which ecclesiastical law and the civil law were one and the same. The Puritans of the 1690s were an incredibly superstitious people; they believed in witches, obviously, but they also thought that the Devil could be lurking behind any tree, within any person, at any time. Thus, it was a time of intense paranoia. This paranoia helps to explain how it was so easy to ignite a hysteria that gained a momentum of its own.
The setting of Act I of The Crucible is the home of Reverend Parris. He is standing over his young daughter, Betty's bed. She lies very still, Abigail tells the reader that the Doctor can find nothing wrong with Betty.
All the action takes place in that upstairs room. Before long, other members of the community arrive, including Rebecca Nurse, John Proctor, Anne Putnam and Reverend Hale, who has been called to Salem by Reverend Parris. Hale is an authority on witchcraft and on helping the bewitched.
All the action takes place in the upper room of Reverend Parris's home. Including, the interrogation of Tituba, Reverend Parris's slave, and her confession to witchcraft. Which is followed by Abigail Williams own admission of having signed the Devil's book.