In 1927 it was purchased by the Jewish Mental Health Society and operated as Hastings Hillside Hospital. Some information on the hospital: http://www.bjpa.org/Publications/downloadFile.cfm...
Society leaving Hastings and relocating to Queens in the early 1940s. The hospital retained the name Hillside Hospital and became a leading research institution in the field of mental health. It merged with Long Island Jewish Medical Center in 1972 – operating under that name today.
Here is a bird-eyes view of the where Hillside Hospital was in relation to the the surrounding streets. 1939 Map
One can still see some pavement and the remains of an old retaining wall in the woods.
The Hillside Hospital move from Hastings was a contentious one with many lawsuits against the Village.
Hillside Hospital fell into disrepair and was demolished in the early 1950s. The Village sold the one acre site where the building stood to the New Rochelle Water Company in 1964. Note the street sign for Chauncey Lane. 1940s