John Janssen (March 3, 1835 – July 2, 1913) was a German-born prelate of the Roman Catholic Church.

He studied at the Royal Theological and Philosophical Academy in Munster, Prussia and the Collegium Augustinianum in Goch, Prussia[1] Janssen was recruited in Munster by French Bishop Henry Juncker in 1858 to serve as a priest in the United States.

[2][3] After immigrating to the United States, Janssen was ordained to the priesthood by Bishop Juncker for the Diocese of Alton in Illinois on November 19, 1858.

[4][2] He received his episcopal consecration on April 25, 1888, from Archbishop Patrick Feehan, with Bishops John Hogan and Louis Fink serving as co-consecrators.

[1] In 1903, at Janssen's request, the Poor Handmaids of Christ religious order set up a hospital in East St. Louis, Illinois.