| NAME | COMPANY | STATUS | SIDE OF MONUMENT |
| O’Brien, Chris. | 44th Reg. Ind. Vol. Inf. | North Side of Monument | |
| Oberlin, George | 155th Ind. Inf. | South Side of Monument | |
| Oberst, Christ. | 44th Reg. Ind. Vol. Inf. | North Side of Monument | |
| Opie, Benjamin | 42nd Ill. Inf. | Died or killed in Service | East Side of Monument |
| Opie, William J. | 44th Reg. Ind. Vol. Inf. | North Side of Monument | |
| Ormsby, Jesse | 42nd Ill. Inf. | Died or killed in Service | East Side of Monument |
| Osborn, Thomas | 12th Reg. Ind. Cal. | North Side of Monument | |
| Otta, Christian | 152nd Ind. Inf. | East Side of Monument | |
| Owens, Andrew | 4th Mich. Inf. | West Side of Monument |