The Roman Catholic Diocese of Sioux City () is the Roman Catholic diocese for the northwestern quarter of the US state of Iowa. The diocese comprises 24 counties in northwestern Iowa, and it covers an area of . The See city for the diocese is Sioux City. It is a suffragan see of the Archdiocese of Dubuque. The cathedral parish for this diocese is the Epiphany. R. Walker Nickless was ordained as bishop of Sioux City on 20 January 2006. History On 24 July 1900, Pope Leo XIII issued a papal bull appointing John J. Keane, former Bishop of Richmond and the first rector of the Catholic University of the Catholic University of America, as Archbishop of Dubuque. This same document provided for the creation of a new diocese by the separation of twenty-four counties in northwestern Iowa from the Archdiocese of Dubuque. The Catholic population of the diocese was about 50,000 people who spoke English and/or German. The first bishop of the Diocese of Sioux City was Irish-born Philip Joseph Garrigan. Garrigan grew up in Lowell, Massachusetts and was ordained 11 June 1870 the Provincial Seminary of New York at Troy. After a short term as curate of St. John's Church, Worcester, Massachusetts, he was appointed director of the Troy seminary for three years, and later pastor of St. Bernard's Church, Fitchburg, Massachusetts. In the fall of 1888 he was appointed the first vice-rector of the Catholic University at Washington, D. C., during the tenure of Keane as rector. Garrigan held the position of vice-rector for fourteen years. He was serving as vice-rector when he was named Bishop of Sioux City on 21 March 1902, and consecrated at the see of his home diocese, Springfield, Massachusetts, on 25 May of the same year, by T.D. Beaven, and on 18 June took possession of his see. Bishop Garrigan designated the not yet completed St. Mary's Church, in the center of the city, as the Cathedral Church of the Diocese. With permission from the Holy See he renamed the church the Cathedral of the Epiphany. Bishop Garrigan carried on an extensive visitation of all the parishes of the diocese. Garrigan died 14 October 1919, and his auxiliary bishop, Edmond Heelan, was appointed his successor. Heelan was born in County Limerick, Ireland and ordained to the priesthood on June 24, 1890. He was rector (1893–1897) of St. Raphael's Cathedral in Dubuque from