The Los Angeles County Sheriff's Department (LASD), officially the County of Los Angeles Sheriff's Department, is a law enforcement agency serving Los Angeles County, California. LASD is the largest sheriff's department in the United States and the third largest local police agency in the United States, following the New York Police Department, and the Chicago Police Department. LASD has approximately 18,000 employees, 9,915 sworn deputies and 9,244 unsworn members. It is sometimes confused with the unrelated Los Angeles Police Department which provides law enforcement services within the city of Los Angeles, which is the county seat of Los Angeles County, although both departments have their headquarters in downtown Los Angeles.

The Los Angeles County Metropolitan Transportation Authority (LACMTA), branded as Metro, is the county agency that plans, operates, and coordinates funding for most of the public transportation system in Los Angeles County, California, the most populated county in the United States.