Two studies were conducted to examine mental representations of loneliness and social connectedness. In Study 1, young adults (N = 2,531) completed the revised UCLA Loneliness Scale (R-UCLA scale) and demographic questionnaires. An exploratory factor analysis of the R-UCLA scale on half the sample revealed a three-dimensional conceptual structure that generalized across gender. This mental representation consisted of correlated facets labeled Isolation, Relational Connectedness, and Collective Connectedness. A confirmatory factor analysis on the other half of the sample corroborated this three-factor solution. In Study 2, a population-based sample of 197 older males and females (M(age) = 57.5 years) completed the R-UCLA scale and measures of objective social circumstances. The confirmatory factor analysis supported the three-factor structure in this diverse and older adult sample. Each facet was uniquely predicted by theoretically related social circumstances. These findings suggest how humans make meaning of their social relationships in their mental representations of loneliness and connectedness.