Background This study examined the influence of built environmental factors in the community on active social network size as well as the moderating influence of different dimensions of social activity on this relationship. Methods This study employed the cross-sectional and correlational approaches to construct a scale measuring key community-level built environment factors and test the moderating influence of social activity on the association between these factors and active social network size in older adults. The study population was all 3,211 older adults who were resident in Accra and were part of the database of the Social Security and National Insurance Trust. Participants were 515 older adults in Accra aged 60 years or more who met some inclusion criteria. A self-reported questionnaire, including a new scale measuring the built environment factors, was used to collect data. Principal component analysis with varimax rotation and confirmatory factor analysis were used to validate the measurement scales, whereas Pearson’s correlation test and multiple linear regression analysis were used to test the associations of interest. Results After controlling for relevant demographic variables, built environment factors in the community have no significant influence on active social network size. Volunteering, support for social ties, and group activity positively moderated the influence of built environment factors on active social network size at p < .05 and β ≥ 0.2. Conclusion The study concludes that social activity is essential to the utilization of available built environmental factors by older adults to make active social ties in the community.