| Name | Residence | Birth Date | Birth Place |
| O'BRIEN, James Abraham | Lander, WY | 15 Sep 1883 | * born United States * |
| O'BRIEN, John Robert | Riverton, WY | 26 Mar 1881 | * born United States * |
| O'BRIEN {OBRINE}, Leo John | Lander, WY | 13 Nov 1887 | Lander, WY |
| O'BRYAN, Clarence Aloysus | Riverton, WY | 27 Nov 1889 | Andover, MO |
| O'CONNOR, John | Lamar, Barton, MO | 21 Mar 1876 | * born United States * |
| O'DONNELL, Joseph Sylvester | Lander, WY | 30 Jul 1885 | * born United States * |
| O'DONNELL, Raymond Patrick | Riverton, WY | 01 Mar 1885 | * born United States * |
| O'MALLEY, John | Riverton, WY | 15 Oct 1885 | * born United States * |
| O'MALLEY, John Joseph | Riverton, WY | 23 Apr 1885 | * born United States * |
| O'NEAL, Charles William | Buffalo, Johnson, WY | 02 Jun 1881 | * born United States * |
| O'NEAL, George Earl | Lander, WY | 30 Nov 1883 | * born United States * |
| O'NEAL, Hugh Darrell | Lander, WY | 19 Sep 1884 | * born United States * |
| O'NEAL, Patrick | Ft. Washakie, WY | 09 May 1892 | Lander, wY |
| O'NEAL, Samuel Reeves | Riverton, WY | 15 Aug 1876 | * born United States * |
| OAKES, Henry Dorsey | Cora, WY | 16 Nov 1882 | * born United States * |
| OAKLEY, Harry A. | Riverton, WY | 10 Mar 1885 | * born United States * |
| OALD, James | Arapahoe, WY | 1878 | * born United States * |
| OBERT, Carl | Lander, WY | 07 Feb 1879 | * born United States * |
| OBERT, Frank Limpes | Lander, WY | 07 Apr 1875 | * born United States * |
| OBLECK, Matt | Hudson, WY | 24 Feb 1893 | Peland, Kroner, Austria |
| OCENAS, Alexander | Hudson, WY | 12 Nov 1881 | * unknown * |
| ODEN, Emil | Lenore, WY | 21 Aug 1895 | Ornskoldsvik, Sweden |
| OFFENBACHER, Phillip Michael | Shoshoni, WY | 09 Feb 1874 | * born United States * |
| OGDEN, Robert Lee | Riverton, WY | 04 Sep 1881 | * born United States * |
| OHARA, Henry Tomoyoshi | Boysen, WY | 08 Aug 1889 | Toyko, Japan |
| OKIE, Howard Fremont | Lost Cabin, WY | 13 Feb 1890 | Lost Cabin, WY |
| OKIE, Van Guelder | Lost Cabin, WY | 12 Aug 1893 | Lost Cabin, WY |
| OLDFIELD, John Clark | Canton, Stark, OH | 13 Jan 1882 | * born United States * |
| OLDHAM, Charles Hancock | Lander, WY | 14 Oct 1880 | * born United States * |
| OLDMAN, Ambrose | Arapahoe, WY | Apr 1897 | Arapahoe, WY |
| OLDMAN, Dominic | Arapahoe, WY | 1878 | * born United States * |
| OLDMAN, Jerome | Arapahoe, WY | 1876 | * born United States * |
| OLDMAN, Josiah | Ft. Washakie, WY | Apr 1878 | * born United States * |
| OLIVER, John Fredrick | Riverton, WY | 16 Feb 1876 | * born United States * |
| OLIVER, John Harvey | Ft. Collins, CO | 19 Mar 1876 | * born United States * |
| OLSEN, Albert E. | Dubois, WY | 24 Sep 1893 | Nemsos, Norway |
| OLSEN, Alfred T. | Dubois, WY | 24 Jan 1887 | Nemsos, Norway |
| OLSEN, Arne Jentoft Leonhart | Riverton, WY | 17 Jun 1892 | Velfporden, Norway |
| OLSEN, Arthur William | Hyrum, UT | 11 Nov 1895 | Hyrum, UT |
| OLSEN, Harold | Dubois, WY | 19 Apr 1894 | Nemsos, Norway |
| OLSEN, Henry, Adalph | Circle, WY | 13 Feb 1881 | * born United States * |
| OLSON, Andrew | Shoshoni, WY | 14 Oct 1884 | * unknown * |
| OLSON, Martin | Dubois, WY | 28 Aug 1880 | * unknown * |
| OLSON, Peter | Dubois, WY | 23 Sep 1884 | * of Sweden * |
| OLSON, William | Dubois, WY | 23 Mar 1883 | * of Norway * |
| ORCUTT {OTCUTT}, James T. | Boulder, WY | 08 Sep 1886 | Meeker, CO |
| ORCUTT, Thomas Howland | Boulder, WY | 25 Jul 1884 | * born United States * |
| ORMESHER, Harry | Riverton, WY | 11 Nov 1880 | * unknown * |
| ORR, Edwin Elsworth | Lander, WY | 19 Dec 1874 | * born United States * |
| ORR, John | Pilot, WY | 03 Jun 1893 | Rosseau, Ontario, Canada |
| ORTIZ, Domingo | Boysen, WY | 08 Aug 1890 | Cueramaro, Mexico |
| ORTUSA, Jose | Lost Cabin, WY | 1882 | * of Spain * |
| OSA, Antonio | Lost Cabin, WY | 10 May 1888 | Itarranguelua, Viscaya, Spain |
| OSHEA, John | Metzler, WY | 29 Sep 1880 | * born United States * |
| OSOVISCKI, Alexander | Dubois, WY | 26 Feb 1886 | * born United States * |
| OSWALD, Thomas Charles Centenial | Lander, WY | 18 Dec 1876 | * born United States * |
| OVERWAY, Joseph | Lander, WY | 19 Feb 1884 | * born United States * |
| OVERY, James Jr. | Lion, Sweetwater, WY | 07 Sep 1883 | * born United States * |
| OWEN, Josiah Tightman | Riverton, WY | 18 Oct 1880 | * born United States * |
| OWENS, Harvey | Long Pine, NE - Fremont County Jail | 30 Jun 1895 | Brown Co., NE |
| OWENS, James Walter | Riverton, WY | 16 Jul 1876 | * born United States * |
| OWENS, William Hazelton | Crowheart, WY | 13 Apr 1900 | * born United States * |
| OWENS, William Newton | Lenore, WY | 18 Feb 1880 | * born United States * |
| OWINGS, Charles Washington | Arapahoe, WY | 20 Mar 1877 | * born United States * |
| OWINGS, Jacob Baltz | Lander, WY | 09 Dec 1873 | * born United States * |
| OWINGS, Robert E. | Moneta, WY | 09 Jan 1886 | Brock, NE |