Nationally representative associations of social determinants of health (SDoH) and health care access metrics with TBI-related mortality are not well described and may differ by age. Using the Centers for Disease Control and Prevention Wide-ranging Online Data for Epidemiological Research platform and other publicly available datasets, we investigated correlations between county-level measures of SDoH (multidimensional deprivation index, social deprivation index, rural-urban continuum codes) and health care access (median distance to nearest emergency department, trauma center, intensive care unit [ICU], number of hospitals and number of hospitals with ICU capability per 1,000 population) with county-level TBI-related mortality overall and stratified by age in the United States from 1999 through 2020. Data from 2,970 counties (95.4% of eligible U.S. counties) were included. We observed a modest correlation of higher county-level TBI-related mortality with greater rurality (ρ = 0.54, 95% CI = 0.52-0.57,