John J. Glennon was the Roman Catholic Archbishop of the Archdiocese of Saint Louis, from 1903 to his death in 1946. He was named a Cardinal several months before his death. Glennon died while returning home just after receiving the traditional red hat.

Glennon's tenure as Archbishop was marred by his active opposition to the racial integration of the city's Catholic parochial schools, colleges, and universities. (See Webster University, Saint Louis University.) After Glennon's death in 1946, the new St. Louis Archbishop, Joseph E. Ritter, moved swiftly to remove barriers to the integration of the city's Catholic educational institutions.

John Glennon was born on 14th June 1862 on a 14 acre (57,000 m²) farm at Hardwood, Kinegad, Co. Westmeath, Ireland. The Cardinal died on 9th March 1964 at Arus An Uachtaran, Dublin

Cardinal Glennon's final resting place is in one of the crypts contained within the mortuary chapel at the Cathedral Basilica of Saint Louis, Saint Louis, Missouri.