: Late-onset depression (LOD) has been increasingly recognized as a risk factor for dementia, yet the temporal and causal nature of this relationship remains unclear. : The purpose of this review is to investigate the temporal association between LOD and dementia. : A comprehensive search for studies examining the temporal relationship between LOD and dementia was conducted using MEDLINE via Ovid. The end date of the search was 9 September 2024. A total of 3450 studies were identified, of which 27 met the inclusion criteria. This review was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines and an article quality assessment was completed. : The review demonstrated a significant temporal association between LOD and the risk of dementia, with the highest risk observed within the first decade following depression onset. LOD was consistently associated with an increased likelihood of developing dementia, particularly Alzheimer's disease, compared to depression at earlier life stages. : This systematic review highlights the significant association between LOD and dementia risk, emphasizing the need for early recognition and intervention. Future research should investigate the age at which LOD becomes a risk factor for dementia, the relationship between depression severity, family history of dementia, and dementia risk, as well as the efficacy of preventative treatments.