Freethought Day is October 12th, the annual observance by freethinkers and secularists of the anniversary of the effective end of the Salem Witch Trials.
The seminal event connected to Freethought Day is a letter written by then Massachusetts Governor William Phips in which he wrote to the Privy Council of the British monarchs, William and Mary, on this day in 1692. In this correspondence he outlined the quagmire that the trials had degenerated into, in part by a reliance on "evidence" of a non-objective nature and especially "spectral evidence" in which the accusers claimed to see devils and other phantasms consorting with the accused.
Note that, contrary to what has been claimed by some, there was no specific order or edict by Phips to ban "spectral evidence" from all legal proceedings. Rather, this was one concern that brought about Phips' stopping the proceedings. When the trials ultimately resumed, "spectral evidence" was allowed but was largely discounted and those convicted were swiftly pardoned by Phips.
In the time leading up to the trials being stopped, it was actually clerics including the famous Cotton Mather, often portrayed as the chief villain in the hysteria, who took the lead in advising cautions against the use of "spectral evidence." The Rev. Increase Mather, Cotton's father, specifically condemned "spectral evidence" in his book 'Cases of Conscience', in which he stated that:
It was this shift in sentiment, no doubt aided by the escalating hysteria and the fact that accusations were beginning to reach higher into the Massachusetts Bay Colony hierarchy, that led to Phips' action.
As Dr. Tim Gorski, Pastor of the North Texas Church of Freethought has observed:
Freethought Week is often observed during the week in which October 12th falls or Freethought Month during October which, of course, culminates in the holiday of Halloween.