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The Federal Government does not ordinarily create or maintain birth, death, marriage or divorce records. Such records are made and kept by state and local governments rather than the National Archives.
In searching for relatives' death certificates, while the names of the parents are helpful, they are not always necessary. Do you know the state that your grandfather died in and the date of death, or at least the year of death? If you know, or partly know, this information, we suggest that you contact the State Archives or Health Department of State to request a copy/and or search for this record. You may wish to note any name variants or broaden your search for the surrounding years.
If you do not know this information, please consider using Genealogy websites such as FamilySearch, or Ancestry, to perform searches for vital records to try to determine the date, but more importantly the State, of death. In addition, the FamilySearch Research wiki for How to Find United States Vital Records may be helpful. Please note that Ancestry is a subscription-based database, but it is available for free public use at all National Archives facilities and many public libraries. FamilySearch is free but you have to create an account with them.
We hope this information is helpful and best of luck with your research!