Encyclopedias, Almanacs, Transcripts, and Maps
- Oiticica, Hélio (1937–1980)
- Ojeda, Alonso de (c. 1466–1516)
- Ojibway
- Ojo Por Ojo
- Okanagon
- Oken, Lorenz (1779–1855)
- Okiek
- Okkaliga
- Olajuwon, Hakeem Abdul
- Olancho
- Olañeta y Güemes, José Joaquín Casimiro (1795–1860)
- Olaya Herrera, Enrique (1880–1937)
- Oldenburg, Claes Thure
- Oldfield, Berna Eli ("Barney")
- Oleneostrovskii Mogilnik
- Olid, Cristóbal De (1488–1524)
- Olinda
- Oliphant, Patrick Bruce ("Pat")
- Olivares, Conde-Duque de (1587–1645)
- Oliveira Lima, Manuel de (1867–1928)