This chapter investigates debates around the First Amendment in the nineteenth century. In 1801, President Thomas Jefferson wrote to the Danbury Baptists of Connecticut that the First Amendment built “a wall of separation between Church & State.” Although not central to interpreting the First Amendment in the nineteenth century, Jefferson’s metaphor became the dominant interpretation in twentieth-century jurisprudence. This chapter examines whether citizens, public figures, and the courts endorsed a theory similar to Jefferson’s, and it finds they did not. Instead, the national practice endorsed public Christianity, building upon that faith’s majority status. At the same time, three groups posed definite challenges to this consensus. Freethinkers raised doubts about both Christianity and its socially privileged status. Roman Catholics had to defend their rights to religious practice. Mormon practice of plural marriage, however, went beyond the population’s willingness to tolerate and so was opposed by the power of the federal government.