Group
- Ophidian Games9
- Optimystical Studios6
- Oracle Sights LLC25
- Orange Sea Turtle Group, LLC1
- Orc Stomp25
- Orc Stomp 5K Fun Run1
- Orcs Unlimited Games27
- Order of the Amber Die7
- Orion Township Public Library1
- Orion Township Public Library & Lake Orion High School1
- Orion Township Public Library / Gina Bucalo-Crowther1
- Orkenspalter TV1
- Oshkosh Gaming Society6
- Osprey Games11
- Otaku RPG Student Group4
- Other Stuff35
- Otherworld Theatre Company1
- Otherworlds Gamers2
- Ottawa Red Shirt1
- Ottawa Red Shirts1,071