Biographical Index of South Dakotans
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| LAST NAME | FIRST NAME | PAGE # |
| Oakes | J A | 7 | 515 |
| Oakes | James A | 5 | 1893 |
| Oakland | J J | 9 | 791 |
| Oaks | Herbert D | 5 | 1565 |
| Oberg | Gustav | 9 | 959 |
| Obermeier | Henry A | 6 | 531 |
| O'Brien | James M | 6 | 956 |
| O'Brien | John J | 6 | 402 |
| O'Brien | M H | 10 | 1246 |
| O'Brien | Thomas | 12 | 97 |
| O'Brien | W S, Hon | 1 | 242 |
| O'Brien | Wm S | 5 | 1366 |
| Ochsenreiter | L G | 10 | 1115 |
| O'Connell | D J | 10 | 51 |
| O'Connell | Daniel | 9 | 577 |
| O'Connell | Edward | 9 | 587 |
| O'Connell | J E | 10 | 153 |
| O'Connell | L A | 9 | 599 |
| Ode | A P | 10 | 526 |
| Odell | Joseph | 2 | 252 |
| Odell | R J | 9 | 762 |
| Oddy | Edward B | 11 | 189 |
| Odell | Archie W | 12 | 232 |
| Odell | Robert J | 12 | 231 |
| Odgle | George | 10 | 285 |
| Odling | Anthony | 12 | 137 |
| Offley | John S | 7 | 796 |
| O'Flaherty | C E, Rev | 5 | 1695 |
| O'Gorman | T J | 9 | 325 |
| O'Gorman | Thomas | 8 | 319 |
| O'Gorman | Thomas | 10 | 340 |
| O'Gorman | Thomas, Rt Rev | 5 | 1133 |
| O'Harra | C C | 10 | 612 |
| Ohlman | M P | 10 | 265 |
| Ohlman | Martin P | 3 | 637 |
| Ohlson | Chas J | 6 | 754 |
| Oien | H H | 9 | 1231 |
| Oien | Joseph | 9 | 1239 |
| Oien | Martin | 9 | 73 |
| Oium | Harris | 7 | 884 |
| O'Keeffe | D J | 9 | 426 |
| Olander | Adolph | 10 | 937 |
| Olander | E A | 10 | 1205 |
| Olander | V C | 9 | 978 |
| Oldfield | Silas R | 6 | 679 |
| Oldham | Charles T | 5 | 1868 |
| Oldham | H T | 3 | 525 |
| Olds | W W | 9 | 272 |
| Olds | Wm H | 6 | 641 |
| O'Leary | Daniel | 5 | 1208 |
| Oleson | Andrew H | 5 | 1666 |
| Oleson | Theodore | 10 | 799 |
| Olin | F A | 6 | 889 |
| Oliver | B N | 9 | 1032 |
| Oliver | Benjamin N | 5 | 1561 |
| Oliver | Bruce | 2 | 369 |
| Oliver | Stephen | 5 | 1834 |
| Olsen | C H | 9 | 124 |
| Olsen | Christian | 3 | 441 |
| Olsen | Eric R | 7 | 294 |
| Olsen | Gust | 9 | 876 |
| Olsen | Len J | 11 | 441 |
| Olsen | M V | 10 | 465 |
| Olsen | Ole P, Hon | 3 | 558 |
| Olsen | Ole, S B | 7 | 1035 |
| Olsen | Peter O, Hon | 3 | 559 |
| Olson | Andrew | 7 | 1093 |
| Olson | Andrew | 9 | 636 |
| Olson | C O | 9 | 887 |
| Olson | David A | 6 | 1103 |
| Olson | E C | 10 | 955 |
| Olson | Edward | 4 | 898 |
| Olson | Edward | 6 | 459 |
| Olson | Erick | 2 | 400 |
| Olson | Eyuar P | 11 | 274 |
| Olson | H O | 9 | 856 |
| Olson | Halvor | 6 | 986 |
| Olson | Hans C | 4 | 618 |
| Olson | Hans I | 7 | 713 |
| Olson | Iver | 7 | 971 |
| Olson | Jacob, Rev | 7 | 863 |
| Olson | James | 2 | 261 |
| Olson | Markus | 9 | 481 |
| Olson | Martin | 9 | 631 |
| Olson | Ole, Jr, Hon | 2 | 239 |
| Olson | Ole J | 7 | 771 |
| Olson | Magnus | 6 | 779 |
| Olson | Peter A | 2 | 434 |
| Olson | Peter O | 4 | 728 |
| Olston | H I | 9 | 287 |
| Olverson | Wm | 6 | 373 |
| Olwin | Anthony H | 5 | 1287 |
| Omdalen | T T | 9 | 254 |
| O'Meara | Wm S, Rev | 4 | 643 |
| Omealy | Hiram L | 6 | 751 |
| O'Neal | J E | 7 | 806 |
| O'Neil | Patrick H | 5 | 1803 |
| Opdahl | Sarah | 7 | 553 |
| Opland | A O | 10 | 731 |
| Opperman | Daniel | 7 | 513 |
| Orcutt | Oran B | 3 | 582 |
| Ordal | J J | 9 | 497 |
| Ordway | Nehemiah G | 4 | 939 |
| O'Reilly | Robert | 2 | 360 |
| Orr | A F | 10 | 581 |
| Orr | Alpha F | 4 | 891 |
| Orr | T G | 10 | 1211 |
| Orstad | Henry O | 5 | 1864 |
| Orth | Peter P | 11 | 482 |
| Orvis | A H | 10 | 399 |
| Orvis | Caroline | 11 | 204 |
| Osbon | O M | 5 | 1354 |
| Osbon | O M, Hon | 7 | 340 |
| Osborne | Warren | 3 | 582 |
| Oschsenreiter | Louis G | 7 | 372 |
| Ostrander | George C | 5 | 1113 |
| Ostroot | Elias G | 7 | 727 |
| Ostroot | G J | 10 | 1000 |
| Otis | Horace | 9 | 395 |
| O'Toole | C S | 9 | 121 |
| O'Tolle | Laurence | 5 | 1115 |
| O'Toole | Lawrence J | 7 | 511 |
| Otte | George B | 11 | 379 |
| Otterly | H L | 9 | 1157 |
| Ottmann | A F | 9 | 921 |
| Otto | Freeman F | 12 | 215 |
| Oulton | Franklin, Dr | 6 | 873 |
| Overby | Samuel O | 5 | 1773 |
| Overgaard | C N | 2 | 390 |
| Overseth | Ole | 2 | 322 |
| Overton | John C | 2 | 380 |
| Oviatt | Samuel W | 5 | 1899 |
| Owen | Garry C | 7 | 544 |
| Owen | John L | 6 | 939 |
| Owens | C H | 10 | 343 |
| Owens | Delia H | 5 | 1563 |
| Owens | Edward | 9 | 690 |
| Owens | Edward W | 2 | 169 |
| Owens | John | 4 | 904 |
| Owens | Matthew | 5 | 1420 |
| Owens | Owen | 9 | 612 |
| Oyan | E J | 9 | 832 |
| Oyen | A I | 9 | 823 |
| Oyen | I I | 9 | 906 |
| Oyloe | O G | 10 | 1029 |