Anti-Masonic Movement, in the history of the United States, popular movement based on public indignation at and suspicion of the secret fraternal order known as the Masons, or Freemasons. Opponents of this society seized upon the uproar to create the Anti-Masonic Party. It was the first American third party, the first political party to hold a national nominating convention, and the first to offer the electorate a platform of party principles.

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The movement was ignited in 1826 by the mysterious disappearance of William Morgan, a bricklayer in western New York who supposedly had broken his vow of secrecy as a Freemason by preparing a book revealing the organization’s secrets. When no trace of Morgan could be discovered, rumours of his murder at the hands of Masons swept through New York and then into New England and the Mid-Atlantic states.

As Anti-Masonic candidates proved successful in state and local elections, politicians saw the issue’s vote-catching possibilities. Anti-Masonic newspapers flourished in the heated political atmosphere. In September 1831, the Anti-Masonic Party held a national convention in Baltimore, Md., nominated William Wirt for president, and announced a party platform condemning Masonry for its secrecy, exclusivity, and undemocratic character.

Wirt won only the state of Vermont (seven electoral votes) in the 1832 election, and the party went into decline after that. By the late 1830s much of its reform impulse had been taken over by antislavery agitation, and most of its politicians had joined the newly formed Whig Party.