O'Connor's papers are primarily from his tenure as Bishop of the Diocese of Newark. These papers are sketchy at best but do include letters to his family while he studied in Louvain, Belgium. Correspondence from Pope Pius X and copies of encyclicals are included in the collection. Visitation ledgers, legal documents relating to real estate transactions and bequests under wills, and episcopal documents relating to incorporation documents and letters concerning personnel questions are included. The papers of O'Connor's Vicar General, Rev. John Sheppard, and his Chancellor, Rev. Thomas Wallace are also in this collection.