Joseph Casimir Plagens (January 29, 1880 – March 31, 1943) was a Polish-born prelate of the Roman Catholic Church. He served as bishop of the Diocese of Grand Rapids in Michigan from 1941 to 1943. Plagens previously served as bishop of the Diocese of Sault Sainte Marie-Marquette in Michigan from 1935 to 1940 as an auxiliary bishop of the Archdiocese of Detroit in Michigan from 1924 to 1935.