The Roman Catholic Diocese of Rockville Centre () is a Latin Church ecclesiastical territory or diocese of the Catholic Church that comprises the territory of Nassau and Suffolk counties on Long Island in the U.S. state of New York, except for Fishers Island, which is part of Suffolk County but is included in the Diocese of Norwich, Connecticut. Founded in 1957, this diocese was created from territory that once belonged to the Diocese of Brooklyn. , it the sixth-largest Catholic diocese in the United States, currently serving approximately 1.5 million people in 134 parishes. The diocese is named for the village where its cathedral, St. Agnes Cathedral, is located, Rockville Centre in Nassau County. The fifth and current bishop is John Barres. The Diocese of Rockville Centre is a suffragan diocese in the ecclesiastical province of the metropolitan Archdiocese of New York. History The Diocese of Rockville Centre was split off from the Diocese of Brooklyn April 6, 1957. St. Agnes Cathedral is the seat of the Diocese of Rockville Centre. (Fishers Island is part of Suffolk County but is included in the diocese of Norwich, Connecticut.) Walter P. Kellenberg, former Bishop of Ogdensburg, served as first bishop of the diocese from 1957 to 1976. He founded the diocese's Catholic Charities office in 1957. Kellenberg was followed by Bishop John McGann, who retired in 2000 and died in 2002. The diocese was led briefly by Bishop James T. McHugh, who died of cancer on December 10, 2000. William Murphy served as the diocese's fourth bishop from 2001 to 2017. Murphy arrived in Long Island from his native Archdiocese of Boston, where he served as the archdiocese's vicar general. He was succeeded by John Barres on January 31, 2017. The Diocese of Rockville Centre currently has no active seminaries within its territory. Its major seminary, the Seminary of the Immaculate Conception in Lloyd Harbor, ceased its seminary program in 2012. In 1984 the Diocese's minor seminary, St. Pius X Preparatory Seminary in Uniondale closed. In 2012 through an inter-diocesan agreement largely made due to the shrinking number of priestly vocations and resources, the Archdiocese of New York, the Diocese of Brooklyn and the Diocese of Rockville Centre, merged their seminary programs. The agreement outlined that the minor seminary programs would be facilitated at the Cathedral Seminary House of Formation in Douglaston, Queens and the major seminary programs would be facilitated at