Objective: Depression and trauma are associated with changes in brain regions implicated in Alzheimer’s disease. The present study examined associations between childhood trauma, depression, adult cognitive functioning and risk of dementia. Methods: Data from 378 participants in the PREVENT Dementia Study aged 40–59 years. Linear and logistic models were used to assess associations between childhood trauma, depression, dementia risk, cognitive test scores and hippocampal volume. Results: Childhood trauma was associated with depression and reduced hippocampal volume but not current cognitive function or dementia risk. Poorer performance on a delayed face/name recall task was associated with depression. Childhood trauma was associated with lower hippocampal volume however poorer cognitive performance was mediated by depression rather than structural brain differences. Conclusion: Depressive symptomatology may be associated with dementia risk via multiple pathways, and future studies should consider subtypes of depressive symptomatology when examining its relationship to dementia.