This study describes cigarette smoking trajectories, the influence of social smoker self-identification (SSID), and correlates of these trajectories in two cohorts of U.S. young adults: a sample from the Chicago metropolitan area (Social Emotional Contexts of Adolescent and Young Adult Smoking Patterns [SECAP], n = 893) and a national sample (Truth Initiative Young Adult Cohort Study [YA Cohort], n = 1,491). Using latent class growth analyses and growth mixture models, five smoking trajectories were identified in each sample: in SECAP: nonsmoking (n = 658, 73.7%), declining smoking (n = 20, 2.2%), moderate/stable smoking (n = 114, 12.8%), high/stable smoking (n = 79, 8.9%), and escalating smoking (n = 22, 2.5%); and in YA Cohort: nonsmoking (n = 1,215, 81.5%), slowly declining smoking (n = 52, 3.5%), rapidly declining smoking (n = 50, 3.4%), stable smoking (n = 139, 9%), and escalating smoking (n = 35, 2.4%). SSID was most prevalent in moderate/stable smoking (35.5% SECAP), rapidly declining smoking (25.2% YA Cohort), and nonsmoking. Understanding nuances of how smoking identity is formed and used to limit or facilitate smoking behavior in young adults will allow for more effective interventions to reduce tobacco use.