• Lottie Oatley (1876 - 1961)
• Anna Josephine O'Brien, nee Brazil (d. 1924)
• Charles Thomas O’Brien (1896 – 1918)
• Colon Henry O’Brien (1894 - 1917)
• Darwin Merle O’Brien (1969 – 2024)
• George Andrew Martin Lane O'Brien (1864 - 1901)
• James Jonathon O’Brien (b. 1894)
• John O'Brien
• Rick O'Brien
• Thomas William O'Brien (1862 - 1916)
• William John “Bill” O’Brien (1878 – 1918)
• Dennis “Dinny” O’Connor (d. ~1939)
• Hubert O'Connor OMI
• Padraig “Paud” O’Donoghue (1922 – 2009)
• Declan O’Donovan (b. 1985)
• Diarmuid O’Donovan (1946 – 2023)
• William Ogilvie (1846 - 1912)
• Alexander Cameron Ogilvy (1930 - 2015)
• Jan Ogilvy (1936 – 2024)
• “Apple Jimmy” Oglow (1867 – 1941)
• Kenneth O'Harra
• Yoneda Okada (d. 1928)
• Dorothy O'Keefe, nee Ogburn
• Peter Olafson
• Old Crow, Zzeh Gittlit / Deetru' K'avihdik (early 1800s - 1869)
• Frances Oles
• Andrew Oleson
• W.H.T. Olive (1865 - 1940)
• Lawrence Olsen (d. 1899)
• Pete Olsen
• Jackie Olson
• John Olson (1930 – 2020)
• Robert Olson (1940 - 2004)
• Marline Yeiko Olson, nee Tamagi (1912 - 1999)
• Lee Olynyk
• Arthur Eugene O’Meara (1859 - 1928)
• Emerson O’Neill (d. ~1921)
• John Arthur William O’Neill (b. 1880)
• John R. O’Neill
• J. Barry O’Neill (d. 1999)
• Hélène Saint Onge
• David Arthur Ordish (1943 – 2024)
• Honora “Diamond Lil” Ornstein (1883 - 1975)
• Michael “Shesley Free Mike” Oros (1952 -1985)
• George Ortell (1872 - 1943)
• Michael James “Mickey” O’Rourke (1878 – 1957)
• Edward S. Orr (1854 - 1926)
• Franklin Herman Osborn (1867 – 1941)
• Harriett Edna Osborn, nee Haines (1872 – 1965)
• Frank H. Osbourne
• John Ostashek (1936 - 2007)
• Al Oster (1925 - 2017)
• Bill Oster (b. 1967)
• Kathyrn "Katie" Lorraine Ostrom (1943 - 2013)
• George Eric Otis (1872 - 1917)