| Ida of Herzfeld, widow and foundress |
| Idesbald, Cistercian Abbot of Ten Duinen |
| Iduberga (Itta, Ida) of Schelde, Wife of Pepin of Landen the Elder |
| Ieron (Ion), of Friesland, Priest, martyred by the Northmen |
| (Clemente) Ignacio Delgado Cebrian, Spanish Dominican Priest, Martyred in Vietnam |
| Ignacy KIopotowski, Priest, Founder of the Sisters of the Blessed Virgin Mary of Loreto |
| Ignatius Brianchininov, Russian monk from Vologda |
| Ignatius Laconi, Capuchin Priest |
| Ignatius Loyola, Founder of the Society of Jesus, Jesuits |
| Ignatius of Antioch, Bishop, Martyr, and Apostolic Father |
| Ignatius of Santhia, Capuchin Priest, who worked in Turin |
| Ignatius Shoukrallah Maloyan, Armenian Catholic Archbishop of Mardin, Martyr |
| Ignatius, Patriarch of Constantinople |
| Igor II, Prince of Kiev |
| Ildefonso Schuster, Cardinal Archbishop of Milan |
| Ildefonsus, Bishop of Toledo |
| Ildemarca (Hilda), Abbess of Fecamp |
| Illidius of Arvernia, Fourth Bishop of Clermont |
| Illuminata of Ravenna, Virgin |
| Illuminatus, Confessor |
| Imelda Lambertini, Dominican Nun |
| Ingenuinus, Bishop of Seben (Tyrol) |
| Innocent, Bishop martyred in Rome |
| Innocentia, Virgin and Martyr |
| Innocentius |
| Ippolito (Hippolytus) Galantini, Lay Man, Founder of the Italian Doctrinaires |
| Irenaeus of Lyons, Bishop, Martyr, and Father of the Church |
| Irenaeus of Rome, Martyr |
| Irenarchus of Sebaste, Martyr |
| Irene of Mount Cornillon, Norbertine Canoness |
| Irene of Rome, friend and healer of St. Sebastian |
| Irene of Tancor, Virgin, Martyred in Thessaloniki |
| Irene, Virgin and Martyr |
| Irmengard, Abbess of Chiemsee |
| Irmina, Abbess of Oeren |
| Iroades |
| Isaac of Dalmatia, Abbot of the oldest monastery in Constantinnople, Patron of the Cathedral of St. Petersburg, Russia |
| Isaac, Abbot of Monteluco, near Spoleto |
| Isaac, Bishop of Armenia |
| Isaac, Martyr |
| Isaac, Syrian Bishop of Nineveh |
| Isabel (Elizabeth), Queen of Portugal |
| Isabelle of France, Sister of St. Louis, Poor Clare Abbess |
| Isaiah, Second Bishop of Rostov |
| Isidore of Chios, Soldier and Martyr |
| Isidore of St. Joseph (de Loor), Passionist lay brother |
| Isidore, Bishop of Seville and Father of the Church |
| Isidore, Farmer |
| Ismidon, Bishop of Die |
| Israel of Dorat, Augustinian Priest, confessor |
| Ita of Killeedy, Irish Abbess, “foster mother of the saints of Ireland |
| Ithamar, First Saxon Bishop of Rochester, England |
| Iuliu Hossu, Romanian Cardinal, Bishop of Cluj-Gheria |
| Ives (Yves, Ivo, Yvo) Helory, of Kermartin, Brittany, Lawyer and Priest |
| Ivo, Bishop of Chartres |
