Previous studies on social isolation and quality of life in single-person households (SPHs) faced limitations in identifying socially isolated groups in a citywide and detailed spatial range. The emergence of big data from various sources offers new possibilities for studying the relationship between SPHs and social isolation. This study examined the spatial distribution of SPHs at high risk of social isolation by age group and the influencing factors for Seoul, South Korea, using Seoul Citizen Life Data. Local indicators of spatial association clustering and spatial econometric models were used for the analyses. The results show, first, that SPHs are concentrated in areas with a high proportion of small- and medium-sized houses and non-apartment-type housing. Second, clear spatial distribution patterns based on life-cycle characteristics exist, with young people clustering near universities and employment centers and older people clustering in residential areas. Third, these life-cycle patterns are not as evident for SPHs with a higher risk of social isolation. Our findings show that not all SPHs can be considered a group with a high risk of social isolation, and the residential patterns of socially isolated SPHs differ from those of typical SPHs throughout their life cycle.