Joseph Casimir Plagens (January 29, 1880 – March 31, 1943) was a Polish-born prelate of the Roman Catholic Church. He served as Bishop of Sault Sainte Marie-Marquette (1935–1940) and then Bishop of Grand Rapids (1940–1943).
Joseph Plagens was born in Czeszewo, near Poznań, to Andrew and Constance (née Grygier) Plagens. At a young age he came to the United States, where he settled in Michigan. He earned a Master of Arts degree from the University of Detroit in 1899, and a Bachelor of Sacred Theology from St. Mary's Seminary at Baltimore, Maryland in 1903.
He was ordained to the priesthood by Bishop John Samuel Foley on July 4, 1903. Plagens then served as a curate at Sweetest Heart of Mary Church in Detroit until 1906, when he became pastor of St. Michael Church in Port Austin. He was named pastor of St. Florian Church at Hamtramck in 1911, and returned to Sweetest Heart of Mary as its pastor in 1919. He was raised to the rank of Domestic Prelate of His Holiness in June 1923.