We examine the relationship between demographics and adherence to certain religious traditions within American Christianity. Starting with Niebuhr's Social Sources of Denominationalism, we interact with a long scholarly tradition that connects demographics and religious groups, particularly the abiding “class-sect” relationship. Included in this literature are works by Roof and McKinney (1987), and the particular profiles of evangelicals by Hunter (1983) and more recently by Smith et al. (1998). Findings indicate slow convergence on certain demographics highlighted by Niebuhr (social class, region, population size), and slow divergence on other demographics (age, percent female, percent married, number of children). Contrary to previous research, evangelical Protestantism is not very distinct demographically; however, black Protestantism is, and this reflects the continued demographic significance of race. Our findings lead us to question accepted theoretical links between demographics and religious groups. We end with some preliminary recommendations for future theorizing in this area.