Traumatic brain injury (TBI) is associated with greater risk and earlier onset of dementia. This study investigated whether later-life changes in subjective cognition and behavior - potential markers of AD - could be observed in cognitively unimpaired older persons with a history of suspected mild TBI (smTBI) earlier in life and whether changes in cognition and behavior mediated the link between smTBI and daily function.Data for 1392 participants from the Canadian Platform for Research Online to Investigate Health, Quality of Life, Cognition, Behaviour, Function, and Caregiving in Aging (CAN-PROTECT) were analyzed. A validated self-reported brain injury screening questionnaire was used to determine history of smTBI. Outcomes were measured using the Everyday Cognition (ECog-II) scale (for subjective cognitive decline - SCD), MBI Checklist (MBI-C, for mild behavioural impairment - MBI), and Standard Assessment of Global Everyday Activities (SAGEA, for function). Inverse probability of treatment weighted logistic and negative binomial regressions were used to model smTBI (exposure) associations with SCD+ and MBI+ statuses, and ECog-II and MBI-C total scores, respectively. Mediation analyses were conducted using bootstrapping.History of smTBI was linked to higher odds of SCD+ (OR=1.45, 95%CI: [1.14-1.84]) or MBI+ (OR=1.75, 95%CI: [1.54-1.98]), as well as 24% (95%CI: [18%-31%]) higher ECog-II and 52% (95%CI: [41%-63%]) higher MBI-C total scores. Finally, SCD+ and MBI+ statuses mediated approximately 45% and 56%, respectively, of the association between smTBI history and poorer function, as indicated by higher SAGEA total scores.smTBI at any point in the life course is linked to poorer cognition and behavior even in community-dwelling older persons without MCI or dementia. Older persons with smTBI may benefit from early dementia risk assessment using tools that measure changes in cognition and behavior. Interventions for declining cognition and behavior may also be beneficial in this population to address functional impairment.