Coadjutor bishop
Ten years after his installation, on April 14, 1869, Bishop Duggan was removed as Chicago bishop and spent the next 29 years living in obscurity in a sanatorium conducted by the Sisters of Charity in St. Louis. The Rev. Thomas Foley, a priest of the Archdiocese of Baltimore, was named Coadjutor bishop and served as Chicago's bishop in his place. Duggan resigned officially as bishop on September 10, 1880 and died at the sanatorium on March 27, 1899. At a time before accurate diagnosis and treatment of mental illness was possible, Duggan was institutionalized on the understanding that he was "hopelessly insane." Today there is no evidence with which to diagnose what exactly he suffered from.