This study investigated the mediating role of neighborhood satisfaction and use of outdoor spaces in the effects of the physical environment on mental well-being. Four planning/design-related aspects of the environment were examined: perceived proximity of home to green/social spaces, open lawn with trees, and building-dominated spaces as well as perceived barriers to neighborhood use. A random sample of 434 Chicago residents participated in a photo survey. The results of linear regression modeling and mediation analyses support the hypothesis that satisfaction with quality of public space and frequency of use of green/social spaces have a significant mediating role in the relationship between nearby environmental attributes and mental well-being. Perceived barriers were also found to have both direct and indirect effects on mental well-being. Recognition of the differential roles played by environmental attributes, neighborhood satisfaction, and use patterns can help guide planners/designers to create outdoor spaces that enhance urban residents’ mental well-being.