True historical events referenced in Elizabeth George Speare's The Witch of Blackbird Pond concern the charter of the Connecticut colony.
In Chapter 7, while engaged in a political quarrel with William Ashby and John Holbrook one evening after dinner, Matthew Wood loudly voices his opinion that the Connecticut colony should be allowed to keep its charter. He voices the following argument to William:
Surrender our charter and we lose all ... . That charter was given to Connecticut by King Charles twenty-five years ago. It guarantees every right and privilege we have earned, the very ground we stand on and the laws we have made ourselves. (Ch. 7)
Matthew's reference to King Charles is indeed historically accurate. In 1662, 25 years prior to the year the novel is set in, 1687, King Charles II generously issued Connecticut colonists a charter that granted the colonists freedom to establish their own government ("The Connecticut Charter," New England Times).
In this same chapter, Matthew also makes the assertion, "King James has no right to go back on his brother's pledge." This is another accurate historical reference since, when King James II succeeded his brother, he established the Dominion of New England, in which he revoked all of the charters of the New England colonies and merged the colonies into the Dominion of New England, over which he would have complete control ("The Connecticut Charter").
Earlier in Chapter 6, Reverend Bulkeley refers to Governor Andros being "appointed by King James," which is another historically accurate reference. King James II appointed Sir Edmund Andros as governor over the Dominion of New England and sent him to revoke the colonists' charters ("What Was the Dominion of New England," History of Massachusetts).
An historical event referenced in Chapter 15 of the novel that is considered more legendary is the hiding of Connecticut's charter. Legend has it that, at the General Assembly meeting in Hartford where Governor Andros announced the revocation of the charter, the candles in the room went out, and the charter was stolen. Legend has it that the charter was stolen by Captain Joseph Wadsworth and hidden in an oak tree just outside of Hartford. But, this event is only considered legendary since we don't really have historical proof of the event ("Hiding the Charter," Connecticut History). Though legendary, the event is firmly believed to have happened.