| Name | Birth Date | Birth Place | Death Date | County | Mother's Maiden Name | Number | Box |
| Oartwieg, Morris George | 12 Oct 1918 | Iowa | 14 May 1921 | Jasper | Loopes | 50-3000 | D2238 |
| O'Brien, Eva Mae | 30 May 1869 | Iowa | 26 Jun 1936 | Jasper | Butrum | A50-0065 | D2796 |
| O'Brien, Paterick | c.1836 | Ireland | 04 Mar 1925 | Jasper | | 50-0990 | D2239 |
| Ochampaugh, Simeon | 15 Apr 1870 | | 12 Oct 1932 | Jasper | | C50-0122 | D2670 |
| O'Connor, Mary | 11 May 1883 | Pennsylvania | 21 Jul 1934 | Jasper | Hogan | E50-0104 | D2732 |
| Ogg, John Wesley | 19 Mar 1838 | Ohio | 11 Jan 1925 | Jasper | | 50-0931 | D2239 |
| O'Hair, Vivian Ann | 16 Apr 1920 | Iowa | 16 Apr 1920 | Jasper | Seibert | 50-2735 | D2238 |
| O'Leary, Cornelius | 20 Sep 1872 | Iowa | 03 Dec 1932 | Jasper | Welch | J50-0098 | D2670 |
| Oliver, Lura | 13 Jan 1891 | Iowa | 29 Jul 1936 | Jasper | Findley | A50-0073 | D2796 |
| Olney, James Monroe | 17 Nov 1866 | Iowa | 31 Oct 1928 | Jasper | Warren | 50-2027 | D2240 |
| Olsen, Hans | 25 Jun 1857 | Norway | 27 Apr 1921 | Jasper | | 50-3001 | D2238 |
| Olson, Cecilia | 13 Jul 1857 | Sweden | 11 Nov 1925 | Jasper | Sjostedt | 50-1122 | D2239 |
| Olson, Edwin | 27 Jul 1894 | Iowa | 08 Mar 1928 | Jasper | Person | 50-1877 | D2240 |
| Olsthoon, Viola May | 03 Aug 1932 | Iowa | 10 Nov 1933 | Jasper | Olsthoon | D50-0167 | D2699 |
| Orcutt, Etta May | 06 Oct 1866 | Iowa | 07 Aug 1930 | Jasper | Thompson | A50-0170 | D2616 |
| Orcutt, Herman Lamorse | 11 Aug 1866 | Iowa | 23 Jan 1927 | Jasper | More | 50-1490 | D2240 |
| Orendorff, Rebecca Maria | 03 Sep 1853 | Indiana | 09 Feb 1929 | Jasper | Cronk | 50-2131 | D2241 |
| Orns, Jacob | 06 Jun 1866 | Iowa | 16 Apr 1931 | Jasper | | B50-0058 | D2643 |
| O'Roake, Danial J. | 25 Nov 1863 | Iowa | 13 Aug 1928 | Jasper | McManenemy | 50-1976 | D2240 |
| O'Roake, Jane | 10 Sep 1856 | Scotland | 20 Jan 1920 | Jasper | Laverty | 50-2629 | D2238 |
| O'Roake, Katherine Phelan | 19 Nov 1886 | Iowa | 08 Sep 1933 | Jasper | | D50-0126 | D2699 |
| Orr, Edward S. | 12 Mar 1875 | Iowa | 13 May 1930 | Jasper | Swihart | A50-0111 | D2616 |
| Orr, Mary R. | 24 May 1860 | Ohio | 29 Jul 1933 | Jasper | Holstetler | D50-0107 | D2699 |
| Orwick, John S. | 10 Nov 1850 | Ohio | 28 Jun 1931 | Jasper | Leonard | C50-0045 | D2643 |
| Osborn, Ellen M. | 04 Dec 1857 | Iowa | 31 Jan 1920 | Jasper | Maggard | 50-2630 | D2238 |
| Osborne, Francis Eugene | 14 Jun 1856 | Iowa | 26 Sep 1931 | Jasper | Inman | C50-0075 | D2643 |
| Osburn, Adolphus | 08 Nov 1862 | Ohio | 18 Jun 1925 | Jasper | McPike | 50-1037 | D2239 |
| Osburn, Edward | 16 Feb 1921 | Iowa | 16 Feb 1921 | Jasper | Neil | 50-3002 | D2238 |
| Osten, Christian Frederick | 01 Aug 1847 | Germany | 08 Jan 1933 | Jasper | | D50-0008 | D2699 |
| Oswalt, Barney Peter | 12 Sep 1840 | Ohio | 25 Oct 1932 | Jasper | | C50-0123 | D2670 |
| Oswalt, William James | 12 Jul 1930 | Iowa | 17 Sep 1933 | Jasper | Henderson | D50-0130 | D2699 |
| Overdyke, Tena | 10 Aug 1889 | Netherlands | 27 Apr 1929 | Jasper | Bierma | 50-2173 | D2241 |
| Owens, Hannah | 10 Nov 1866 | England | 04 Mar 1929 | Jasper | Elliott | 50-2152 | D2241 |
| Owens, Lettie Nadine | 08 Aug 1923 | Iowa | 01 Dec 1929 | Jasper | Hoover | 50-2325 | D2241 |
| Owens, Rose Marie | 26 Sep 1900 | Iowa | 23 Dec 1931 | Jasper | Dobrkosky | C50-0113 | D2643 |
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