In 1925, concerned about rising crime rates, the County Board of Supervisors voted to create the Nassau County Police Department, replacing a scattered system of constables and town and village police departments. Consisting initially of Chief of Police (later Commissioner) Abram Skidmore, 55 officers and a fingerprint expert, the force grew to 450 officers by 1932 and reached 650 officers by the time Skidmore retired in 1945.
The expansion accelerated dramatically following World War II with the rapid suburbanization of the county. It reached 1,000 officers in six precincts by 1950. A seventh precinct was opened in 1955 and an eighth followed five years later. In the early 1970s, with crime and civil disorder in neighboring New York City and other cities a major concern, the force was boosted to its greatest strength, nearly 4,200 officers. Since then, it has declined to around 2,600, making it still one of the largest county police agencies in the United States.