Background: Associations between religious involvement and substance use are well established. However, limited research examines the effects of religious affiliation, informal participation, and network support on substance use among two distinct age cohorts. Objectives: This study aims to examine whether religious affiliation, informal participation, and network support are associated with alcohol, tobacco, and marijuana use among young and late middle-age adults. Method: The UC Berkeley Social Networks Study (Wave 1, 2015) offers novel cohort data on young (21-30 years old, n = 483) and late middle-age (50-70 years old, n = 673) adults. Poisson regression models were used to predict alcohol use, while logistic regression models were used to predict odds of smoking and marijuana use. Results: Among young adults, membership in a religious organization was associated with less alcohol, tobacco, and marijuana use. Conversely, participating in informal organizations was associated with more alcohol and marijuana use. Desiring more people to talk to and get together with were associated with more smoking and drinking, respectively. However, wishing more people to ask for help was associated with less substance use altogether. In a similar pattern, among older adults, religious involvement was associated with less alcohol and marijuana use. Desiring more people to ask for help was also related to less marijuana use. Conclusion: Younger adult participation in informal groups serves to encourage social substance use. In contrast, older people are more involved in religious groups, which support social behaviors that do not include substance use.