| Name | Type | Circle | Bench | Formed | Notes |
|---|---|---|---|---|---|
| Oberbronn | County | 1622: Partitioned from Leiningen | 1665: Annexed to Rickingen | ||
| Oberehnheim | Imperial Free City | ||||
| Obermünster in Regensburg Obermunster in Regensburg | Abbacy | Bav | 1500: Bavarian Circle 1793: Council of Princes | ||
| Obernai | Imperial City | Upp Rhen | 1648: Annexed to France | ||
| Oberried | Provostry | ||||
| Oberstein | HRE Lordship HRE County | 1682: Line died out | |||
| Ochsenhausen | 1391: Abbey | Swab | 1495: Became "reichsfrei" (territorially independent) 1793: Council of Princes 1803: Secularized 1806: Annexed to Wurttemberg | ||
| Odenheim | Provostry | Upp Rhen | |||
| Offenburg | Imperial City | Swab | SW | 1289 | 1803: Mediatized to Baden |
| Olbruck | HRE Lordship | ||||
| Oldenburg ''Grand Duke of Oldenburg, Heir in Norway, Duke of Schleswig, Holstein, Stormarn, Ditmarshes & Oldenburg, Prince of Lubeck and Birkenfeld, Lord of Jever and Kniphausen" | County 1774: Duchy 1829: Grand Duchy | Low Rhen | PR | 1101 | 1181: Counts obtained HRE Princely rank 1667: Main Oldenburg line died out 1676: To Christian V of Denmark 1773: To Grand Duke Paul of Russia 1871: Joined German Empire |
| Oppeln | Duchy | ||||
| Orange | 1000s: County 1173: Principality 1376: HRE Principality | Upp Rhen | 1000s: Split off from Countship of Provence | 1150: Division into 2 princely lines 1289: Lines reunited 1417: To Chalons dynasty 1530: To Nassau dynasty 1660-1665: French occupation 1673-1702: French occupation 1713: To France | |
| Orange-Nassau See Nassau-Orange | |||||
| Orlamünde | County | 1032 | 1015: Annexed to Weimar | ||
| Orlamünde | County | 1170: Partitioned from Ballenstädt | Partitioned several times 1411: Annexed to Meißen | ||
| Orlamünde-Gräfenthal | County | 1295: Partitioned from Orlamünde | 1321: Partitioned into Orlamünde-Lauenstein, Orlamünde-Weimar and Orlamünde-Wiehe | ||
| Orlamünde-Gräfenthal-Lichtenkamm | County | 1406: Partitioned from Orlamünde-Lauenstein | 1426: Annexed to Meißen | ||
| Orlamünde-Lauenstein | County | 1321: Partitioned from Orlamünde-Gräfenthal | 1406: Partitioned into Orlamünde-Gräfenthal-Lichtenkamm, Orlamünde-Lauenstein-Schaunforst and Orlamünde-Lichtentanne | ||
| Orlamünde-Lauenstein-Schaunforst | County | 1406: Partitioned from Orlamünde-Lauenstein | 1467: Annexed to Saxe-Wittenberg | ||
| Orlamünde-Lichtentanne | County | 1406: Partitioned from Orlamünde-Lauenstein | 1460: Annexed to Saxe-Wittenberg | ||
| Orlamünde-Plassenburg | County | 1285: Partitioned from Orlamünde-Weimar | 1340: Annexed to Meißen | ||
| Orlamünde-Weimar | County | 1100: Partitioned from Weimar 1139: Annexed to Ballenstädt 1170: Recreated on partition 1365: Annexed to Meißen | |||
| Orlamünde-Wiehe | County | 1321: Partitioned from Orlamünde-Gräfenthal | 1372: Annexed to Meißen | ||
| Orsini and Rosenberg Prince of Orsini and Rosenberg, Baron of Lerchenau and Grafenstein | 1681: HRE Count (Personalist) 1790: HRE Prince (Personalist) | n/a | FR | 1681 | 1200s: Family 1st mentioned 1684: Adopted style of "Orsini-Rosenberg" |
| Ortenau | Landgraviate | ||||
| Ortenburg Count of Ortenburg, Count and Lord of Tambach | 1805: HRE County | 1048 | 1141: 1st use of "Count of Ortenburg" 1395: Partitioned into Ortenburg-Altortenburg (extinct 1446), Ortenburg-Dorfbach (extinct 1462) and Ortenburg-Neuortenburg 1417: Imperial estate 1418/19: Line of counts died out; passed to Counts oc Cilli 1500: Bavarian Circle 1805: Ceded to Bavaria | ||
| Ortenburg-Altortenburg | 1395: County | 1395: Partitioned from Ortenburg | 1446: Annexed to Ortenburg-Dorfbach | ||
| Ortenburg-Carinthia | County | 1100s: Created from the Ortenburger and Sponheimian territories in Carinthia | 1660: Annexed to Austria | ||
| Ortenburg-Dorfbach | County | 1395: Partitioned from Ortenburg | 1462: Annexed to Ortenburg-Neuortenburg | ||
| Ortenburg-Neuortenburg | County | 1395: Partitioned from Ortenburg | |||
| Osnabrück Osnabruck | Bishopric | Low Rhen | EC | 783: Bishopric 1226 | 1793: Council of Princes 1803: Secularized to Hanover 1813: Annexed to Hanover |
| Osterberg | Lordship | 1540: Partitioned from Kronburg | 1745: Renamed to Rechberg and Rothenlöwen | ||
| Öttingen Ottingen | 1147: County 1674: HRE Prince | Swab | 1141 | 1423: Partitioned into Öttingen-Flochberg, Öttingen-Öttingen, Öttingen-Spielberg and Öttingen-Wallerstein 1522: Division into Ottingen-Ottingen and Ottingen-Wallerstein | |
| Ottingen-Baldern | 1798: Line extinct; passed to Ottingen-Wallerstein | ||||
| Öttingen-Flochberg | County | 1423: Partitioned from Öttingen | 1549: Annexed to Öttingen-Öttingen | ||
| Öttingen-Öttingen | County; 1674: Principality | Swab | 1423: Partitioned from Öttingen | 1731: Line extinct; annexed to Öttingen-Wallerstein | |
| Öttingen-Spielberg | County; 1734: Principality | 1423: Partitioned from Öttingen-Wallerstein | |||
| Öttingen-Wallerstein | County; 1774: Principality | Swab | 1423: Partitioned from Öttingen | 1623/1694: Division into Ottingen-Baldern, Ottingen-Spielberg, Ottingen-Wallerstein | |
| Ottobeuren | Abbacy | ||||
| Overijssel | Lordship | Burg | 1512: Burgundian Circle | ||