Courtesy of FiveThirtyEight, this graph shows the increase since 2001 in the number of people worldwide who live in jurisdictions where gay same-sex (or homogamous, if you prefer) marriage is legal. As of 2010, roughly 250 million people live in such areas (each column represents the total number for that year, broken into individual colors to show the number in each region):
The spike in 2008 is due to the California courts recognizing same-sex marriages, so the U.S. data pushed the total number upward; that, of course, was quickly reversed by Prop 8, so that bump disappears in 2009. Currently within the U.S., same-sex marriages are legal in Vermont, New Hampshire, Iowa, Connecticut, Massachusetts, and Washington, D.C., while apparently New York, New Mexico, California, and Rhode Island don’t allow them to be performed but recognize those performed elsewhere (a friend of mine who lives in Rhode Island couldn’t marry his boyfriend there, but drove a half hour from their home into Massachusetts to do so and then went home, where his out-of-state marriage was then entirely legal). California recognizes those same-sex marriages that occurred between June and November 2008, before Prop 8 passed. Within Europe (which is all thrown together here, unfortunately), as far as I know the specific countries where it’s legal are Sweden, Norway, the Netherlands, Belgium, Spain, Portugal, and Iceland), with Portugal and Iceland both doing so this year. In Mexico, same-sex marriages are legal only in Mexico City, but if performed there, must be recognized in other areas. And Argentina became the first country in South America to legalize them just last Thursday. (I’m not including domestic partnerships and other arrangements that are somewhat equivalent to, but clearly distinguished from, marriage here; adding those would certainly increase the number significantly.)
This is a small percentage (about 3.7%) of the total global population of nearly 7 billion, and they are highly concentrated in (Western) Europe and North America, with those in Africa, Asia, and Central and South America largely excluded. But the global pattern is a slow but steady rise over time just over the past decade in the recognition of same-sex marriages.