Despite the importance of community service for the well-being of individuals and communities, relatively little is known about the developmental course of community service during the transition to adulthood (TTA). This study tested competing hypotheses about change in community service across the TTA by estimating latent growth models from Ages 18 to 26 in a national U.S. sample. Analyses tested for cohort differences in community service and for individual differences in developmental trajectories by socioeconomic status, gender, grades, religiosity, race/ethnicity, college expectations, and college degree attainment. Using Monitoring the Future data from 1976 to 2011, the best-fitting latent growth model for community service was quadratic: Community service declined from Ages 18 to 24 and leveled off thereafter. Cohort differences in intercepts indicated that Age 18 community service increased over historical time; developmental declines in community service were consistent over 4 decades. Parent education predicted higher Age 18 community service but not growth parameters. Community service trajectories varied by gender, high school grades, religiosity, college expectations, and educational attainment, although all groups declined. Findings contribute to civic developmental theory by clarifying age and cohort effects in community service. Rising levels of community service at Age 18 may reflect heightened focus on service in high schools or the role of other socialization forces, yet these increases do not mitigate the decline across the TTA. We highlight the need for rethinking the ways in which institutions and communities can better support youth community service during the TTA.