The Edmunds Act, also known as the Edmunds Anti-Polygamy Act of 1882,[1] is a United States federal statute, signed into law on March 23, 1882 by President Chester A. Arthur, declaring polygamy a felony in federal territories, punishable by "a fine of not more than five hundred dollars and by imprisonment for a term of not more than five years".

The Edmunds Act also prohibited "bigamous" or "unlawful cohabitation" (a misdemeanor),[3] thus removing the need to prove that actual marriages had occurred.

[1] The act not only reinforced the 1862 Morrill Anti-Bigamy Act but also made the offense of unlawful cohabitation much easier to prove than polygamy misdemeanor and made it illegal for polygamists or cohabitants to vote, hold public office, or serve on juries in federal territories.

The Supreme Court ruled, in Murphy v. Ramsey, 114 U.S. 15 (1885), that the statute was not ex post facto because convicts were charged for their continued cohabitation, not for the prior illegal marriage.

The issue went to the U.S. Supreme Court in the case Late Corp. of the Church of Jesus Christ of Latter-Day Saints v. United States, which upheld the Edmunds–Tucker Act on May 19, 1890.