The changing landscape of same-sex marriage Proponents of same-sex marriage have had a string of successes around the country since the Supreme Court struck a key part of the Defense of Marriage Act in U.S. v. Windsor in June 2013. As a result of Monday's Supreme Court action, 24 states, plus the District of Columbia, now allow or could allow same-sex marriage, and 26 states prohibit it. Read related stories. Select a state on the right to learn more about the status of same-sex marriage. * Same-sex marriage allowed A solid majority of Americans support same-sex marriage, according to a Washington Post-ABC News poll conducted in June. The survey shows that 56 percent of Americans support it and 38 percent oppose it.