Most obituaries are not indexed. Thus, you need to provide an exact date of death in order for anyone to go through the old newspapers for an obituary. Have you checked the 1905 state census to see whether George COOPER was living then? That is available at the State Historical Library, 900 Governors Drive, Pierre, SD 57501. (They charge a fee, which keeps going up, so I don't know the current one.) If he was living for the 1905 census, then you should be able to get a death certificate from the SD Dept. of Health, 523 E. Capitol, Pierre, SD 57501-3182. SD Death Certificates were required from mid-1905. The State Historical Library also had the WPA Cemetery Project papers, which show most of the early burials, but many are only from the tombstone records, which might have only the year. Another source of a death date could be a church or funeral home, but you have to know which one. You might try to get the homestead application papers. GLORecords show that he patented in Aurora County, 103-66, 9 SE, very close to the town of White Lake. Further records would show when the land was sold (Register of Deeds, Court House, Plankinton, SD 57368).