Charles Williams - Source for Charles Williams death date and location?

Does anyone have a source(s) for when and where Charles Williams died?

All known genealogy sites do not have sources attached to his death date or location.

His wife Flora F Hunter death certificate from Rosebud Montana states he was the informant and that his address was also Rosebud Montana.

However, the area cemeteries, mortuaries and local/state governments do not have a death record for him.
Some have stated that a death in rural areas of that time did not always get recorded in government records, which makes sense.