Objectives The purpose of this study was to examine the association between social capital and depression in adults in their 20s. Methods The study used data from the Community Health Survey 2019 (CHS 2019). The CHS 2019 covered a representative sample of 229099 adults from 17 census tracts in the Republic of Korea, of which 19589 adults in their 20s were taken as subjects for this study. The subjects completed a survey with questions regarding demographic characteristics, built environment and social capital. The symptoms of depression were evaluated through the Patient Health Question-naire (PHQ)-9. Multiple logistic regression was used to examine whether social capital was asso-ciated with depression. Results The multiple logistic regression results indicated that social capital was associated with depression in adults in their 20s. When demographic characteristics and built environment were included in the analysis, trust, contact with relatives, contact with friends, and social activities were associated with depression in adults in their 20s. Conclusion A lack of social capital was associated with depression in Korean adults in their 20s. Our study suggests a need to look beyond individual factors to intervene in national and community social capital and prevent depression in adults in their 20s.