Sheriff
In the American west, the Spanish were colonizing what would become Texas, California. The equivalent of the sheriff was called an Alguacil (sheriff/constable). As Americans moved west, they often started new communities. A sheriff was usually the only available law enforcement. Sheriffs had the power of posse comitatus. That means a sheriff had the power to deputize anyone to help him keep the peace or go after and arrest criminals. A group of temporary deputies under the authority of a sheriff is called a posse. As America grew the posse was used less and less. Sheriffs are still the main law enforcement in rural areas.