Objective <p>This study aimed to assess the association between sedentary behavior (SB) and dementia among the general adult population.</p> Methods <p>We queried PubMed, Web of Science, Embase, and Cochrane Library from their inception to November 3, 2024. Two authors independently extracted the data from i<Emphasis Type="Underline">n</Emphasis>cluded studies, including hazard ratios (HRs) and their 95% confidence intervals (CIs), to assess the risk of dementia among individuals with SB. The quality of included studies was assessed using the Newcastle–Ottawa Scale. We used a random effects model if <i>I</i>² &gt; 50% and <i>p</i> &lt; 0.10; otherwise, a fixed-effect model was used. In addition, we assessed publication bias by funnel plot, and performed leave-one-out sensitivity analysis.</p> Results <p>We included ten cohort studies, nine of which were of high quality. Our analysis demonstrated an increased risk of dementia among individuals with SB (pooled HRs, 1.17; 95% CIs, 1.06–1.29). Individuals with high sedentary time (ST), defined by TV viewing, demonstrated a 31% increased risk of dementia compared to those with low ST (pooled HRs, 1.31; 95% CIs, 1.25–1.37). No significantly increased risk for dementia was observed among individuals with high computer usage time (pooled HRs, 0.89; 95% CIs, 0.73–1.09). However, when SB was defined by other methods, individuals with high ST demonstrated a 33% increased risk of dementia compared to those with low ST (pooled HRs, 1.33; 95% CIs, 1.25–1.42).</p> Conclusion <p>SB increases the risk of dementia, but SB defined by computer usage time has not shown this association.</p> Trial registration <p>CRD42023493109.</p>