Earls, Counts | Titles by Rank
- Counts of Olivais
- Counts of Olivares
- Counts of Olivares
- Counts of Olivares
- Counts of Oliveira dos Arcos
- Counts of Olivença
- Counts of Oliveto
- Counts of Ollone
- Counts of Olocau
- Counts of Oñate
- Counts of Oncieu de Chaffardon
- Counts of Oncieu de Chaffardon
- Counts of Ongnies
- Counts of Ons en Bray
- Counts of Oppersdorff
- Counts of Oppersdorff-Solms-Braunfels
- Counts of Oppido
- Counts of Orange-Nassau
- Counts of Orbe
- Counts of Oreno
- Counts of Orgaz
- Counts of Oria
- Counts of Oriola
- Counts of Orlamünde
- Counts of Orleans
- Counts of Ornano
- Counts of Oropesa
- Counts of Orsay
- Counts of Orsini und Rosenberg
- Counts of Orssich
- Counts of Ortenburg
- Counts of Ortenburg-Neuortenburg
- Counts of Orx
- Counts of Osborne
- Counts of Osilo
- Counts of Osona
- Counts of Osorna
- Counts of Osorno
- Counts of Ossona
- Counts of Osternburg
- Counts of Ostervant
- Counts of Ostheim
- Counts of Ostrorog
- Counts of Otrante
- Counts of Ottenburg
- Counts of Ottolini
- Counts of Oultremont
- Counts of Oultremont de Wegimont
- Counts of Oultremont de Wégimont et de Warfusée
- Counts of Ourém