The Willard Plan refers not to a building plan, but more a State plan of Asylum system administration. The plan put forward the idea that a state should move it's chronic insane patients from regular mental hospitals and almshouses to institutions built purely for custodial care of the chronic insane.
The plan was named after Dr Willard, the man who proposed this idea to the New York legislature in 1861. At the time the mental hospitals of many states were becoming dangerously overcrowded due to the chronic insane. This crowding due to incurables led to less effective treatment for acute patients and as a result a decreased chance of their recovery. Many Chronic patients were sent to their county or city almshouses from the state hospital, often living in deplorable conditions. To combat this problem Dr. Willard felt a state hospital for custodial care would be best, both providing the chronic insane with a humane existence, and also freeing up space at the State Hospital at Utica. This proposition caused much debate in the AMSAII, with many favoring building accommodations for chronic patients on current hospital grounds and arguing the ethics of giving up on treatment of those declared "incurable". Dr. Kirkbride was among them and vehemently objected to it. In the end however the motion passed 7-6 and New York adopted the Willard plan. While Dr. Willard died before his plan became reality the Willard State Asylum was named in his honor.
Many states eventually created hospitals for the chronic insane at some point. Some of these hospitals were Willard State Hospital, Binghamton State Hospital,Tewksbury State Hospital, Rhode Island State Hospital, and Wernersville State Hospital to name a few.
There is no architectural standard to hospital built on the Willard Plan. Many were established in previously established buildings, architecture and design were less important as no treatment would take place at those institutions. Willard State Hospital was originally opened in a former four story agricultural college building and later a large kirkbride, followed by a series of two story "mini kirks" scattered around the campus. The Binghamton Asylum for the Chronic Insane was opened in what was the New York Inebriate Asylum, a single linear building. Tewkburry in Massachusetts and the State Asylum for the Incurable Insane in Rhode Island were two custodial asylums which grew out of almshouses. Meanwhile the State Asylum for the Chronic Insane of Pennsylvania at Wernersville was purpose built on a popular asylum plan.