The United States federal government has recognized as legally valid the April 1975 same-sex marriage of Richard Adams and Anthony Sullivan, approving the “green card” petition that Adams filed in 1975 for his husband, an Australian citizen. After Adams died in December 2012, Sullivan sought to have the Immigration Service recognize their marriage and grant a green card to him as the widower of a U.S. citizen.
http://thepridela.com/2016/06/united-states-government-says-gay-couples-1975-marriage-is-valid/