Northwood is an area in the London Borough of Hillingdon, West London, located 14+1⁄2 miles northwest of Charing Cross. Northwood was part of the ancient parish of Ruislip, Middlesex. The area was situated on the historic Middlesex boundary with Hertfordshire, and since being incorporated into Greater London in 1965, has been on the Greater London boundary with that county. It has also been within the Metropolitan Police District since 1840.