Regulators

Vigilantism was prevalent in America for many years after the Civil War, and the vigilante actions often had political overtones left over from the war. Nowhere was this truer than in Missouri. A slave-holding border state that remained in the Union, Missouri was very divided during the war, and the bitterness engendered by the conflict lingered and gave rise to violence long after the war officially ended. Although not an act of what we would normally think of as vigilantism, the killing of Rev. Samuel S. Headlee, which I discussed last time, is an example of an act of violence that occurred shortly after the war and had political overtones. Rev. Headlee was killed by Union men in large part because he was an unrepentant and outspoken Confederate sympathizer.
About the same time that Headlee was killed in the western edge of Webster County in late July of 1866, another drama that definitely did involve vigilantism was winding down in neighboring Greene County. In fact, the Regulators, formed earlier in the year to combat an outbreak of thievery that centered around the Walnut Grove area of northwest Greene County, held a mass meeting on the very day that Headlee was killed, although there was no apparent connection between the two events.
The Regulators, who disbanded shortly after the mass meeting, were something of an exception to the idea that vigilante groups tended to be politically motivated. Although the Regulators were made up mostly of Union men and many of the lawbreakers that they opposed had been Confederate guerrillas or at least Southern sympathizers, the first victim of the Regulators was Green B. Phillips, a former captain in the Enrolled Missouri Militia who had aided in the defense of Springfield during John S. Marmaduke's attack on the town in January of 1863. There is also little evidence to suggest that Phillips had seriously violated any laws. However, he had apparently fallen in with the thieves and was therefore lynched for befriending the wrong people.
You can read more about the Regulators in my book about Ozarks gunfights and other notorious incidents.