A site was identified within the Brentwood Hall Estate for the construction of an asylum. The asylum was designed by Kendall & Pope in the High Victorian Gothic style to a corridor plan layout. The foundation stone was laid on in October 1851 and the hospital was officially opened as the Essex County Lunatic Asylum in September 1853. Extensions included three country style homes in 1863, a new block for female patients in 1870 and another large block for male patients in 1888. A new chapel was added in 1889 and a new nurses' block in 1900.