Early-life environment is related to childhood brain development and cognitive function in later life. However, the associations of early-life risk factors with dementia and cognitive impairment were still controversial. Our study aims to investigate early-life risk factors for dementia and cognitive impairment. PubMed and Cochrane Library were searched to identify prospective cohort and retrospective case-control studies exploring early-life factors for dementia and cognitive impairment. Pooled effect estimates for each factor were calculated by random-effect model. Thirty-seven studies with 46,727 participants were included. The pooled results indicated significant associations of dementia with food deficiency (OR = 2.05, 95% CI = 1. 22-3.44), low education level (RR = 1.80, 95% CI = 1.60-2.02), and shorter leg length (OR = 1.19, 95% CI = 1.07-1.32). Other potential risk factors identified in the systematic review include rural residence, number of siblings, history of head trauma, early parental death or re-marriage, and poor learning ability. Early-life factors, including education level, leg length, history of childhood head trauma, family-related factors and learning ability, were associated with the risk of dementia and cognitive impairment in later life. Further high-quality longitudinal studies are needed to verify the causality between early-life risk factors and dementia and cognitive impairment.