With New York state's passing of same-sex marriage legislation on June 24, 2011, one in nine Americans now live in states where gay men and lesbians can marry. If the state of California, with its 37 million population, carries out last year's appellate ruling overturning Prop 8, the number will double. Presently (2011), 10 countries allow same-sex marriage. The largest is South Africa, with a population of 50 million, followed by Spain (47 million) and Argentina (41 million). The US's six states and Washington, DC. have a combined population of 35 million, ranking it after Argentina and just ahead of Canada.
265 million people (as of 2011) worldwide now live in countries/jurisdictions where same-sex couples can marry - 4% of the world's 6.8 billion people (besides the US states and DC, Mexico City is also included). And although many more countries may legalize same-sex unions before the US, at least some individual US states can be counted among these socially progressive nations.
I've written two previous posts on the subject of same-sex marriage: