Warley Hospital was a hospital for the mentally ill located in Brentwood, Essex, England. Warley Hospital was built in Victorian High Gothic style using red and black bricks, had stone mullion windows, and octagonal towers. It was closed in 2001 and has since been redeveloped as private residences.
The hospital was originally destined for Chelmsford and plans were drawn up as early as 1819, for a hospital for the mentally ill, serving south Essex.
The Hospital was opened in 1853  (believed to be on 23 September) as the Essex County Lunatic Asylum serving the whole county. The original buildings, accommodating up to 500 people, were designed by H. E. Kendall in a Tudor style, of red brick with black stone detailings.
By 1858 the hospital had 450 patients and in 1920 it became known as Brentwood Mental Hospital, being renamed again in 1953 as Warley Hospital.
The hospital was several times enlarged in the 19th and the earlier 20th century, and by 1937 had 2,000 beds. 
It was used as a long-stay psychiatric hospital, but in its later years most patients seemed to be ordinary people who had suffered breakdowns. It was closed in 2001, with the patients and staff moving to other areas.
It is an urban myth that in order to provide discreet access to and from the hospital the builders included an underground tunnel from the town's railway station up the hill to the hospital; this tunnel was alleged to be accessible to hospital staff as recently as 1990 although the railway end had long been closed down. In truth, no such tunnel ever existed.
The institution was finally closed down in January 2011. Much of the area has now been redeveloped as a residential area with 300 homes, although some of the architecture of the original asylum still stands in the form of The Galleries, developed by City & Country, a luxury development consisting of converted apartments.