OOPS! I Goofed!
Roosevelt Co. wasn't created until Feb. 18, 1919. Poplar in 1902 was located in Valley County which was created Feb. 6, 1893.
You can contact the Opheim Community Library, 100 Rock St., Opheim, MT 59250-0108 or 406-762-3213 and ask if they have obits back to 1902.
Contact the Valley County Clerk & Recorder, www.valleycountymt.net/schools.html
and ask if they have any death records from 1902.
You also might want to contact the Pioneer Museum of Valley County, valleycountymuseum.com/Home.html who has "an extensive genealogical archives and Western Reading Room. . ." Successful Searching!