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Objectives To investigate the association of loneliness and its component subscales with the risk of dementia in a general Japanese older population. Method A total of 1,141 community-dwelling Japanese residents aged ≥65 years without dementia were prospectively followed up for a median 5.0 years. We evaluated any loneliness and its component subscales—namely, social and emotional loneliness—by using the 6-item de Jong Gierveld Loneliness Scale. Cox proportional hazards models were used to estimate hazard ratios (HRs) of each loneliness type on the risk of dementia controlling for demographic factors, lifestyle factors, physical factors, social isolation factors, and depression. Results During the follow-up, 114 participants developed dementia. The age- and sex-adjusted incidence rate of dementia was significantly greater in participants with any loneliness and emotional loneliness than those without. The multivariable-adjusted HRs (95% confidence intervals) of participants with any loneliness and emotional loneliness on incident dementia were 1.61 (1.08–2.40) and 1.65 (1.07–2.54), respectively, as compared to those without. However, there was no significant association between social loneliness and dementia risk. In subgroup analyses of social isolation factors, excess risks of dementia associated with emotional loneliness were observed in participants who had a partner, lived with someone, or rarely communicated with relatives or friends, but such association was not significant in participants who had no partner, lived alone, or frequently communicated with friends or relatives. Discussion The present study suggested that loneliness, especially emotional loneliness, was a significant risk factor for the development of dementia in the general older population in Japan.