| John O'BANION (????-????) | & | Sarah BRADLEY (????-????) |
| William O. O'BANION (1873-1963) | & | Mandy Augusta GREENFIELD (1997-1970) |
| August OBERKROM (1864-1945) | & | Mary LEFFMANN (1870-1938) |
| Caleb Hall O'BRYAN (1827-1902) | & | Mary Catherine ROBINSON (1826-1899) |
| Elvin Perry O'BRYAN (1899-1957) | & | Opal Lucile KOCHENDARFER (1913-1987) |
| General Ivy O'BRYAN (1881-1961) | & | Sarah TURNER (1886-1966) |
| Silas Wright O'BRYAN (1854-1937) | & | Mary Emaline HEWGLEY (1854-1939) |
| Wellington Floyd ODER (1893-1971) | & | Clara Caroline BOHS (1902-1999) |
| Samuel Ray OFFUTT (1844-????) | & | Julia Ann FINKS (1846-1885) |
| Jeremiah O'HANLON (1790-1867) | & | Margaret SCANLON (1793-????) |
| Andrew OLIPHANT (1820-1900) | & | Elizabeth HOOKER (1826-1896) |
| Newton Sherman OLIVER (1862-1947) | & | Nancy Ella COE (1864-1933) |
| John Wesley ORAHOOD (1827-1908) | & | Mary F. BILDERBACK (1837-1905) |
| Ephraim L. ORR (1831-1910) | & | Melissa A. WEEKS (1843-1875) |
| William M. ORR (1851-1914) | & | Malinda E. ALEXANDER (1849-1910) |
| John OSBORN (1805-1864) | & | Rachel LEMON (1805-1888) |
| John OSBORN (1830-1918) | & | Elizabeth BELL (1835-1889) |
| John Friedrick Wilhelm OSICK (1826-1899) | & | Anna Marie NOLTING (1829-1872) |
| Zacharias OSICK (1794-????) | & | Anne Mariew Louise BAUMANNS (1798-????) |
| Edward T. OWEN (1796-1880) | & | Rachael ROMAN (1797-1880) |
| John James OWEN (1834-1910) | & | Kerin WALKER (1840-1866) |
| William OWEN (1766-1843) | & | Martha "Patsy" (1777-????) |
| Benjamin F. OWENS (1827-1880) | & | Sarah Sareen 'Sary' TAYLOR (1827-1900) |
| Melville Lee OWENS (1877-1928) | & | Margaret Elen RHOADES (1867-1955) |
