The Middlesex County Asylum was founded in 1898 with the hospital designed in a country estate style in 1900 by architect Rowland Plumbe, who also rebuilt, to his designs, the Royal London Hospital, Whitechapel in 1897.
The hospital was designed for 1,205 residents, and the grounds were designed by William Goldring. Following the construction of the numerous buildings and extensive grounds, Napsbury opened on 3 June 1905. According to the Middlesex County Record, the initial cost, including land and equipment, was £545,000, or £473 per bed. In 1908 Plumbe designed an extension to accommodate a further 600 patients.
During the First World War, Napsbury was used for and known as the County of Middlesex War Hospital, which treated wounded soldiers. Following the war, the hospital was returned to its original purpose, and, in the late 1920s, a nurses' home was also added to the site.
The Asylum today:
After the closure of the hospital, Crest Nicholson acquired the site and built the current residential development sympathetically around the existing wood and parkland areas. Now consisting of approximately 500 residences spread over newly built detached, terraced and townhouses also apartments converted from the original buildings. Features include multi-use tennis courts, cricket and sports pitches, a sports pavilion building and footpaths throughout the extensive woodland.