Purpose <p>Interest in social networks has increased in recent decades amid concerns around social isolation and loneliness, despite increased access to social connections via electronics. Prior studies identified predictors and outcomes linked to network size, but few studies have examined age, period, and cohort effects simultaneously.</p> Methods <p>Using four decades of data, we assessed age, period, and cohort effects, as well as sociodemographic and personality factors, on family and friend network size. In 1981, 3,481 participants (<i>M</i>_<i>age</i> = 47.8 years; 62% White; 38% female) were sampled from East Baltimore, with follow-up periods beginning in 1993, 2004, and 2021. Mixed effects models tested fixed effects of age, sociodemographic, and personality characteristics, along with random effects of period and cohort, on network size.</p> Results <p>Results demonstrated that males, unmarried persons, and persons higher on neuroticism had smaller family networks; Non-White individuals and those higher on conscientiousness had smaller friend networks. Higher income, education, and extraversion predicted larger family and friend networks. No age or cohort effects were detected, though a period effect indicated larger friend networks during baseline data collection compared to other periods.</p> Conclusion <p>Findings suggest family and friend networks are shaped by demographic and personality traits but remain largely stable across time and generation.</p>