The Anti Horse Thief Association was an important citizen-based crime fighting outfit in the Old West. It got its start in the late 1850s, battling marauders and bandits in Kansas. It spread to many states and territories over the next 60 years and included a national constitution and bylaws. They denied being vigilantes.
By 1906, the AHTA counted more than 30,000 members, who believed membership helped prevent theft of livestock and more. Numbers began dropping after the Old West days, and the group became more of a fraternal and social organization.