In legalizing same-sex marriage, Vermont joins its neighbors, Massachusetts and Connecticut, which are also traditionally liberal states.
New Hampshire and New Jersey permit civil unions. California, Oregon and Washington allow domestic partnerships, which extend many of the benefits of marriage.
And now, reports CBS News correspondent Priya David, same-sex marriage advocates say it's even gaining traction in the nation's heartland.
Iowa's state supreme court last week declared unconstitutional a law denying marriage for same-sex couples.
Mary Evans and Stephanie McFarland are celebrating.
"Iowa, and Iowans," says Evans, "have always come down on the side of fairness. Justice is alive and well in Iowa."
New York-based advocacy group Lambda Legal filed the Iowa lawsuit.
"It's very important for people across the country,' says Lambda's Kevin Cathcart, "to realize this is not something that only happens on the East Coast or the West Coast, but that actually gay people actually have and deserve equal rights across the country."
A recent CBS News poll found that 33 percent of Americans support same-sex marriage, up from 22 percent back in 2004.
Younger people increasingly support it: Forty-one percent of those under 45, compared to just 18 percent of those over 65 years of age.
So, will same sex marriage ever be recognized by all 50 states?
"Even if public opinion keeps moving in the direction, it's sort of slowing-moving," says Joe Matthews of the New America Foundation. "It's not something that's going to happen in a couple of years. It's gonna take 10 years or 20 years before you see broad recognition of same-sex marriage."
Still, David points out, many people believe marriage is strictly between a man and a woman.
"It's really clear," asserts Maggie Gallagher, of the National Organization for Marriage, "that, if you leave it up to the American people, they would say, to make a marriage, you need a husband and a wife, and we don't want politicians messing with it."
The day when the whole country embraces same-sex marriage may indeed be may be a long way off, David observes: Twenty-nine states have voted for a constitutional ban. And Californians recently voted to eliminate same sex marriages, though that vote is being contested in the courts.