It might not be coincidence that Williamsburg was the first city in the US to have a dedicated psychiatric hospital. Sightings of odd happenings around President Harkaway’s residence might account for the admission of No-Majs who were, in fact, perfectly sane.
-- History of the Magical Congress of the United States (Pm)
The earliest psychiatric facility in the United States was founded in Williamsburg, possibly due to No-Maj sightings of a vicious pack of Crups owned by MACUSA President Thornton Harkaway (Pm).
The psychiatric hospital in Colonial Williamsburg was known as the "Public Hospital for Persons of Insane and Disordered Minds" and, just as stated on Pottermore, was the first building in the U.S. dedicated to helping the mentally ill. Governor Francis Fauquier founded the institution in 1773 in hopes of curing "persons who are so unhappy as to be deprived of their reason." Unfortunately the place was more like Azkaban prison than a hospital:
The building housed 24 cells, all designed for the security and isolation of their occupants. Each cell had a stout door with a barred window that looked on a dim central passage, a mattress, a chamber pot, and an iron ring in the wall to which the patient's wrist or leg fetters were attached. By the theories of the day, mental illnesses were diseases of the brain and nervous system, and the mentally ill chose to be irrational. Treatment consisted of restraint, strong drugs, plunge baths and other "shock" water treatment, bleeding, and blistering salves. An electro-static machine was installed. Between 1773 and 1790, about 20 percent of the inmates were discharged as cured.
In 1790, fences 10 feet high and 80 feet long were added to each end to provide exercise yards for both sexes, and staircases were built at the ends of each hall. In 1799, two dungeon-like cells were dug "under the first floor of the hospital for reception of patients who may be in a state of raving phrenzy." Source: Colonial Williamsburg Foundation
From the Web
Pottermore: Magical Congress of the United States (MACUSA) by J.K. Rowling
Williamsburg Foundation Almanack: Public Hospital
Public Hospital for Persons of Insane and Disordered Minds on Harry Potter Wiki