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Vigilantes. Vigilante committees were made up of citizens who arrested, tried, convicted, and punished individuals.
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Sheriffs. The first formal law enforcement agency to emerge in the territories beyond the Mississippi was the sheriff's office.
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State police. The first territorial police agency established in the United States was the Texas Rangers. Originally, the Rangers were a corps of fighters who fought in the Texas revolution against Mexico in 1835. Later, the Rangers evolved into a law enforcement agency. Pennsylvania formed the first modern state police in 1905. Within the next 20 years, state police became common. For the most part, early state police broke up labor strikes and performed other duties that local police were unwilling or unable to do.
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U.S. Marshals. Federal marshals constituted the oldest federal law enforcement agency, established in 1789. In the 19th century, horseback‐riding marshals made arrests, served court papers, managed federal prisoners, and conducted the U.S. population census.