Chapin began his medical career under Dr. John Swett, an attending physician at New York Hospital.
He returned to Canandaigua, New York to practice at Brigham Hall, a private mental hospital.
By the mid-nineteenth century, the New York State Medical Society was interested in the care of insane people in the counties’ almshouses.
Existing laws and practices provided that people who had been insane for a year or more could be committed to local almshouses by the state’s courts, where there was little medical care and poor living conditions.
In 1865, the Legislature authorized such an institution and mandated that insane people would no longer be committed to counties’ almshouses.
[3] Chapin was appointed by the New York State Governor to a committee to select a site for the new facility.
In 1884, following the death of Dr. Thomas Kirkbridge, the first physician-in-Chief of the Department of the Insane of the Pennsylvania Hospital, Chapin was named the new chief physician and remained there for 23 years.