While much progress has been made in understanding the demographic determinants of mortality in the United States using survey data, the lack of population-level register data is a barrier to further advances in mortality research. With the release of Social Security application (SS-5), claim, and death records, the National Archives and Records Administration (NARA) has created a new administrative data resource for researchers studying mortality. We introduce the Berkeley Unified Numident Mortality Database (BUNMD), a cleaned and harmonized version of these records. This publicly available dataset provides researchers access to over 49 million individual-level mortality records with demographic covariates and fine geographic detail, allowing for high-resolution mortality research. All code for replication are available on the linked Github repository: https://github.com/caseybreen/bunmd The BUNMD dataset is publicly available for download here: https://censoc.berkeley.edu/