Mary Walcott is depicted as an adult woman, played by actress Janet Montgomery, who was almost thirty in the first season. In reality, Mary Walcott was only 16 when the witchcraft crisis started in Salem.
John Alden is portrayed as a young man, being played by actor Shane West who was in his mid thirties when the show started. In reality, Captain John Alden, Jr. was in his mid 60s at the time of the witch trials.
Tituba is portrayed as black, being played by British actor Ashley Madekwe, who is of African descent. In reality, Tituba was consistently described as "Indian" in records of the time, and so was almost certainly Native American.