Introduction To examine associations of history of traumatic brain injuries (TBIs) with loss of consciousness (LOC) with dementia incidence and memory decline. Methods We studied 2718 participants from the 1992 enrollment cohort of the Health and Retirement Study (HRS) aged 65 years or older in 2000. History of TBI with LOC was self‐reported in 1992. Dementia was assessed using four algorithms established in HRS. Participants were followed from 2000 to 2014 with repeated measures of dementia and memory performance. Cox models and linear mixed‐effects models were used. Results In 1992, 11.9% of the participants reported a history of TBI with LOC. In fully adjusted models for all four algorithms, participants with a history of TBI with LOC had no statistically significant difference in dementia incidence nor in memory decline, compared to participants without TBI history. Discussion Our study did not find evidence of a long‐term association between history of TBI with LOC (of unknown frequency and severity) and dementia incidence or memory decline.