According to the About page for the Association of Religion Data Archives, "The Association of Religion Data Archives (ARDA) strives to democratize access to the best data on religion. Founded as the American Religion Data Archive in 1997 and going online in 1998, the initial archive was targeted at researchers interested in American religion. The targeted audience and the data collection have both greatly expanded since 1998, now including American and international collections and developing features for educators, journalists, religious congregations, and researchers. Data included in the ARDA are submitted by the foremost religion scholars and research centers in the world. Currently housed in the Social Science Research Institute, the College of Liberal Arts, and the Department of Sociology at the Pennsylvania State University, the ARDA is funded by the Lilly Endowment, the John Templeton Foundation and the Pennsylvania State University."
This website has a bunch of great articles and facts that can help you learn more about your ancestor's religion. From the homepage, click on the button on the left labeled The Learning Center. Under Learning Resources check out Research Tools.
Under Research Tools you will find information about American religious denominations including a family tree which shows where different denominations came from and groups that are outgrowths, including the Baptists, Lutherans, Mennonites, Methodists, Presbyterians, UCC, and the Restoration Movement. Information such as statistics and surveys are also part of this section of the website. Check out the Religion Dictionary located in the Learning Center for definitions having to do with religious terminology and churches.