Many Americans exhibit declining religiosity during early adulthood. There is no consensus about why this occurs, though longstanding assumptions suggest the secularizing effects of higher education, normative deviance and life course factors. We evaluate these effects on decreasing frequency of religious practice, diminished importance of religion and disaffiliation from religion altogether. Results from analyses of the Add Health study indicate that only religious participation suffers substantial declines in young adulthood. Contrary to expectations, emerging adults that avoid college exhibit the most extensive patterns of religious decline, undermining conventional wisdom about the secularizing effect of higher education. Marriage curbs religious decline, while cohabitation, nonmarital sex, drugs and alcohol use each accelerate diminished religiosity – especially religious participation – during early adulthood.