The St. Louis County Police Department (SLCPD) is the primary and largest law enforcement agency serving St. Louis County in the U.S. state of Missouri. The current Chief of Police is Colonel Kenneth Gregory. According to the Charter of St. Louis County, the county police chief has all of the criminal law enforcement duties of the sheriff of St. Louis County, except for the operation of the St. Louis County Jail, which is handled by the St. Louis County Department of Justice Services (civilian), court bailiff and service of civil process. Court bailiff/civil process duties are provided by a court-appointed sheriff and his employees, none of whom have law enforcement powers.

St. Louis County Police Department is the Largest County police agency in Missouri, based on number of employees, county population, and geographic area served.