Sixty years ago, five Sisters of Mercy left their convents in Brooklyn to start an exciting innovative plan: to staff a Catholic co-educational high school on the East End of Long Island called Mercy. It is obvious that God's Providence has directed our beloved school throughout the course of its history.
In 1956, Sr. Mary Euphrasia, Superior General of the Sisters of Mercy in Brooklyn and Long Island, missioned five Sisters to Riverhead. Mercy High School opened its doors to welcome its first forty-seven students. Sr. Mary Theopane, the Principal, and Srs. Mary Hugh, Gilbert, Liguori and Hilary, became the core of a new world.
Mercy High School was housed in a temporary building on Roanoke Avenue, and continued to develop. When more room was needed, St. John's Parish offered the use of two unused classrooms. Meanwhile a building program was set in motion. Contracts were signed with Sr. Mary Anita's father, William J. Boegel as architect and Lawrence J. Rice as builder. Ground was broken in 1959.
In September 1961, although not yet completed, Mercy opened its spacious portals to seven classes of excited students: a Sophomore class, a Junior class, a Senior class and four incoming Freshman classes. Since the main and lower floors of the structure were not ready for use, all these students were accommodated by the classroom space on the second floor. Bishop Kellenberg, Bishop of the newly formed Diocese of Rockville Centre, dedicated the completed building in October of 1962.
As the years passed, the school continued to grow steadily. Following Sr. Mary Theopane as first principal, were Sr. Mary Geraldine, Sr. Julia Smith, Sr. Mary Noreen, Sr. Joan Delap, Mr. Michael Kramer, Mrs. Gene Fellingham, Sr. Elaine Hanson, Dr. Steven Cheeseman and Dr. Carl Semmler, the current principal. The number of faculty has grown from the first five Sisters to a faculty of over fifty professionals.
In September 1994, the Mercy educational mission was expanded to include 7th and 8th graders.
In 2002, a new partnership was created with the Diocese of Rockville Centre and the Sisters of Mercy. In September 2003, Mercy was officially renamed Bishop McGann-Mercy Diocesan High School by Bishop William Murphy, honoring Bishop John R. McGann the second bishop of the Diocese of Rockville Centre.