The purpose of this study was to determine the influence of knowledge and beliefs on beneficial behaviors and dementia risk scores. A online survey was conducted among Chinese community residents over 18 years old. Multivariate logistic regression was used to identify the impact of knowledge and beliefs on dementia risk scores and beneficial behaviors. The respondents were 760 adults (mean age = 47.6 years, 60.8% female). Knowledge and beliefs were associated with cognitive activities (knowledge, odds ratio [OR] = 1.04; beliefs, OR = 1.17) and dementia risk scores (knowledge, OR = 0.95; beliefs, OR = 0.82). Additionally, lower perceived susceptibility (OR = 1.68; 95% CI, 1.04 to 2.72) and higher perceived benefits (OR = 0.68; 95% CI, 0.57 to 0.80) were associated with lower dementia risk scores. Knowledge and beliefs can promote beneficial behaviors and reduce dementia risk. In particular, perceptions of dementia susceptibility and benefits should be enhanced, which will greatly reduce dementia risk in the general public.