The Haun's Mill massacre was an event in the history of the Latter Day Saint movement. It occurred on October 30, 1838 when a militia unit from Livingston County attacked a Mormon settlement in eastern Caldwell County, Missouri, United States, in retaliation for the killing of one Missourian and mutilation of another, as well as attacking Missouri State Troops, at the Battle of Crooked River. By far the bloodiest skirmish in the 1838 Mormon War in Missouri, the events have long been remembered by the members of the Latter Day Saint movement. The fifty-five men known by name to be involved were never prosecuted.