By 1860, the number of persons in the U.S. who practiced spiritualism was probably at least four million. In 1853, John Edmonds stated, “Believers in spiritual intercourse are now numbered by millions on earth.”^ In 1855, the North American Review cited a New England Spiritualists’ Association address, printed in 1854, that claimed “nearly two millions of people in our nation…are already believers in Spiritualism.” The North American Review article, which expressed sober concern about spiritualism, did not consider the New England Spiritualist’ Association’s claim to be an overestimate.^ Other sources indicate about a million spiritualists in the U.S. about 1855.^ Theodore Parker, a Unitarian minister who considered spiritualism to be fraudulent., observed in 1856 that spiritualism was growing rapidly.^ A Catholic Convention in Baltimore in 1859 put forward an estimate of 11 million spiritualists, a figure that a spiritualist writer repeated in 1869 with an attributed date of 1867. John Edmonds, who carefully collected, analyzed, and presented statistics as a founder of the Prison Association of New York, provided the following analysis:

in a letter to the “Spiritual Magazine” of London, dated May 4, 1867, {John Edmonds} estimated the number of Spiritualists in the United States, five years ago, at ten million. In a recent letter to myself {Robert Owen} he has reiterated the conviction that he had good authority for such a calculation : adding that he feels assured it is under, rather than over, the truth.^

In 1874, the number of spiritualists in the U.S was estimated at four million persons “who believe in Spiritualism and whose minds are never lifted from its delusion.”^ The U.S. Civil War years (1861-1865) were probably the years in which spiritualism was most popular.

Spiritualists in 1860 plausibly numbered more than a third of the number of members of Christian churches. The United States’ population in 1860 was 31 million. Members of Christian churches, including children, amounted to about 37% of the population, or 12 million persons.^ Based on available estimates, spiritualists probably numbered more than four million in 1860.

Persons who practiced spiritualism and members of Christian churches weren’t necessarily mutually exclusive groups. What identified spiritualists among spiritual persons and persons of tradition religious faith was spiritual communication along with individualism (no organized body of the faithful) and claims to science, empiricism, and public knowledge (anyone can try it and test if it works).