On July 13, 1967,
Pope Paul VI appointed him as the Bishop of Sokoto. He was consecrated a bishop by Cardinal
John Cody of
Chicago on August 15, 1967, at St. Pius V Church in Chicago. The principal co-consecrators were Archbishop
John Kwao Amuzu Aggey of
Lagos and Chicago auxiliary bishop
Aloysius John Wycislo. He was installed as the diocesan bishop in
Sokoto on October 1, 1967, and continued to serve there until his resignation was accepted by
Pope John Paul II on December 3, 1984. Before his appointment as bishop there were anti-
Igbo and anti-Christian riots in 1966 that left the diocese of Sokoto without most of its people, its only indigenous priest fled, and many of its church buildings were destroyed. He focused on the northern part of his diocese, where the people remained, and opened the first secondary school in
Gusau in 1968. The civil war ended in 1970 and the Catholic people began to return to the Sokoto diocese. The oil industry expanded in the 1970s and that helped to increase the size of the diocese. The Dominican sisters opened a house in Gusau. The catechetical school at
Malumfashi trained catechists for northern Nigeria. Successful evangelization efforts were made among the
Hausa people. Good relations were maintained with Muslims and other Christian churches. Dempsey suffered several minor strokes toward the end of his time as bishop. He was also the only non-Nigerian bishop in the country. He had to check in and out with the police when he left
Sokoto State to enter
Katsina State, which was also a part of the diocese. ==Later life and death==