In this community‐based cohort, levels of neuronal degeneration (NfL) and astrogliosis (GFAP) biomarkers remained elevated for 12 to 14 years after TBI, and AD‐related plasma biomarkers (inverted Aβ42/Aβ40 ratio and pTau181) remained elevated for 8 to 9 years after TBI. Here, GFAP is linked to Alzheimer disease.