Limited research has explored the relationship between falls, cognitive decline, and dementia onset in older adults with aging. Therefore, this study aimed to investigate the impact of cognitive function on the development of dementia and explore the association between falls and dementia among older adults. This study utilized data from the Korean Longitudinal Study of Aging, which tracked a sample group at 2-year intervals from the initial wave in 2006 to the eighth wave in 2020. Among the older adults (≥60 years) surveyed, 2829 were included in the analysis, and cognitive function and number of falls per year were recorded. We hypothesized that these variables were associated with dementia and tested the variables using dementia diagnosis data. The participants were assigned to either a dementia group (dementia diagnosis) or a control group (no dementia diagnosis). Analyses were performed to enhance generalizability of the hypothesis to all participants (≥45 years, n = 7130). Cognitive decline and dementia incidence increased with aging among older adults. The dementia group had a significantly higher rate of cognitive decline than the control group, as well as a higher number of falls and magnitude of annual changes in falls. The changes in falls were irregular regardless of cognitive function. Furthermore, falls were associated only with the development of dementia, not cognitive function. Similar trends were observed across the total participant group. Our findings highlight the importance of monitoring cognitive function and falls as potential markers for predicting dementia onset in older adults. •We studied the association between falls and dementia in older adults.•Older adults with dementia showed a rapid increase in cognitive decline.•Significant correlation was found between cognitive decline, falls, and dementia.•Cognitive function and falls in older adults are markers of dementia.•Multifaceted approaches are needed to prevent dementia in older adults.