Name is followed by the page number(s) in the Atlas on which they’re found.
| Oameg, C. 56, 60 |
| Oathoat, Jno. 79 |
| O’Brien, J. 83 |
| O’Brien, Jno. 48 |
| Ochs, F. 79 |
| O’Connell, R. 52 |
| O’Connell, Wm. 52, 56 |
| O’Conner, Jno. 51, 52 |
| O’Connor, Susan 38 |
| O’Donnell, A. 41 |
| O’Donnell, James 48 |
| O’Donnell, Jno. 51 |
| O’Donnell, M. E. 56 |
| Oehlertz, F. 44 |
| Oeschger, John 41 |
| Officer & Pusey 26 |
| Officer, T. 91 |
| Officer, Thos. 26, 41 |
| Ohlertz, Fritz 70 |
| Okeif, Thos. 84 |
| Olderog, August 23 |
| Olds, J. 43 |
| Olendorf, E. 27 |
| Oliver, Mrs. 38 |
| Olsen, Geo. 91 |
| Olsen, J. 44 |
| Olsen, Peter 84 |
| Olson, Geo. 84 |
| Olson, H. 84 |
| Olson, Hans 84 |
| Olson, Mark 84 |
| Olson, N. 83 |
| Oltman, J. M. 79 |
| Omeg, C. 60 |
| O’Neil, J. 44 |
| O’Neill, James 48 |
| ones, M. E. 91 |
| Orcult, C. 48 |
| Orcut, C. 29 |
| Orcutt, C. 83 |
| Orr, Anthony 48 |
| Orr, Wm. 24, 38 |
| Orton, B. D. 30 |
| Osborn, G. 41 |
| Osborn, J. L. 41, 56 |
| Osborn, J. W. 41, 56 |
| Osborn, O. 56 |
| Osborn, W. P. 75 |
| Osborn, Wm. 52 |
| Oschenbine, W. 63 |
| Osler, Alexander 12 |
| Osler, Calvin 12 |
| Osler, Elwood 12 |
| Osler, G. 12 |
| Osler, J.K. 12 |
| Osler, Jno. 12 |
| Osler, Milton 12 |
| Osler, Mrs. D. 12 |
| Osler, Sam’l 12 |
| Osler, Wm. 12 |
| Ostdick, G. 79 |
| Ostdick, Jno. 79 |
| Osterick, G. 79 |
| Otta, C. 63 |
| Otto, Herman 48 |
| Otto, W.J. 12 |
| Ouren, H. 23, 37 |
| Owen, F. M. 41 |
| Owen, T. R. 41 |
| Owens, F. M. 38 |
| Owens, J.R. 12 |
| Owens, T. 60 |