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- Ida of Boulogne, Countess of Mortain, 1204–1216
- Ide-Raymonde of Forez, Countess of Forez
- Ilaria Scillato, Lady of Ceppaloni
- Ingeborg of Norway, Regent of Norway 1319-1326 and Sweden 1319-1324 during the minority of her son.
- Ippolita I Ludovisi (1663–1724), Princess of Piombino, 1700-1724
- Irene the Athenian, Byzantine Empress, 797-802
- Irene Palaeologina, Empress of Trebizond, 1340–1341
- Irmgard of Plotzkau (1070/80-1153), Heiress of County of Walbeck
- Irmgard of Wevelinghoven (d.1474), Heiress of Lordship of Alfter
- Isabeau of Antoing (d.1354), Burgravine of Ghent
- Isabeau of Carlat, Viscountess of Carlat, 1303-?
- Isabeau of Carlat, Lady of Carlat
- Isabeau of Craon, Lady of Craon
- Isabeau of Germaines (d.1341), Lady of Germaines
- Isabeau of Ghistelle, Countess of Harnes, 1386-1413
- Isabeau of Thouars, Lady of Mauleon & Talmond, Viscountess of Thouars, Countess of Benon & Dreux
- Isabeau of Vivonne, Lady of Regnac
- Isabel, widow of Ravano dalle Carceri, Lord of Euboea, 1209–1216; Princess of Euboea, 1216-1220
- Isabel of Aragon (1409–43), Countess of Urgell, 1433–1443
- Isabel de Mauduit, heiress of County of Warwick
- Isabel Douglas, Countess of Mar, Countess of Mar and Lady of Garioch, 1391-1404
- Isabel Teles de Molina (1290-?), 10th Lady of Menezes
- Isabel de Warenne, heiress of Warenne
- Isabella I of Castile, Queen of Castile, 1474–1504
- Isabella of England (1332–1379), Countess of Soissons, 1365
- Isabella, Duchess of Lorraine
- Isabella II of Spain, Queen of Spain, 1833–1868
- Isabella of Gloucester (1170–1217), Countess of Gloucester
- Isabella of Ibelin, Lady of Beirut, 1264-1282.
- Isabella of Jerusalem, Queen of Jerusalem, 1190–1206
- Isabella of Oultrejourdain, Lady of Oultrejourdain
- Isabella Appiani, also known as Isabella d'Appiani d'Aragon, Lady of Piombino & Elba, 1590–1594; Princess of Piombino, 1594-1661
- Isabella Pallavicini, Marchioness of Bodonitsa, 1278-1286
- Isabella of Roucy, Countess of Roucy, ?-1379
- Isabella of Spain (1566–1633), Countess of Charolais, 1598–1633, Countess Palatine of Burgundy, 1598–1633
- Isabella of Taranto, Princess of Taranto, 1463–1465
- Infanta Isabella Clara Eugenia of Spain
- Isabella de Warenne (1137–1199), Countess of Surrey.
- Isabella da Ponte, Heiress of Tagliacozzo
- Isabelle of Albret (d.1294), Lady of Albret & Viscountess of Maremne, 1283–1294
- Isabelle, Lady of Argos and Nauplia
- Isabelle of Angoulême (1187–1246), Countess of Angoulême, 1202–1246
- Isabelle of Beaujeau (d.1297), Lady of Beaujeau, 1250-1297
- Isabelle of Beauvau (1436–1474), Lady of La-Roche-sur-Yon, Lady of Champigny-sur-Vende
- Isabelle of Blois (d.1236), Lady of Chateaurenault & Countess of Chartres, 1218-1236
- Isabelle of Brienne (1305–1360), Countess of Conversano, 1356–1360, Countess of Lecce, 1356–1360, Countess of Brienne, 1356–1360.
- Isabelle of Coucy (d.1411), Countess of Soissons, ?-1411
- Isabelle of Dreux (1160–1239), Lady of Baudemont
- Isabelle of Foix (1360–1426), Viscountess of Béarn & Castelbon & Countess of Foix, 1398-1412
- Isabelle of France (1158–1197), Countess of Vexin
- Isabella, Countess of Vertus (1348–1373), Countess of Vertus 1361-1373
- Isabelle of Luxemburg (d.1472), Countess of Guise
- Isabelle of Mayenne (d.1257), Lady of Mayenne, 1220-1257
- Isabelle of Rumigny (1263–1322), Lady of Rumigny, 1270–1322
- Isabelle I of Villehardouin (1260–1311), Princess of Achaea, 1289–1297, 1301-1307
Read more about this topic: List Of Female Rulers And Title Holders