Dressed in everything from formal suits and traditional white gowns to T-shirts, the couples began saying "I do" at midnight to the cheers and applause of family, friends and supporters.
"To us, we always felt married. But we didn't have equality," said Cindy Golden, just moments after saying her vows at the Manhattan city clerk's office and formally taking the name of her partner of 16 years.
"I didn't think it would ever happen," Sophia Golden said, "to see it happen in this lifetime."
The National Organization for Marriage held rallies attended by thousands in New York City, Albany, Buffalo and Rochester.
Protesters said Gov. Andrew Cuomo and state lawmakers had redefined marriage without giving voters input, as they have been allowed in other states.
Cuomo campaigned in support of gay marriage, which he called a basic human right, and lobbied the Legislature hard before its historic June 24 vote to legalize it.
Across from his Manhattan office Sunday, a crowd that started with several hundred people swelled to thousands, and protesters waved signs saying "Excommunicate Cuomo" and "God cannot be mocked."
In Niagara Falls, the city made the most of its nickname, the Rainbow City. The rainbow is a recognized symbol of gay pride, and Niagara Falls, with its Rainbow Bridge to Canada, Rainbow Boulevard and Rainbow-themed businesses, hopes to attract some of the business same-sex weddings will provide.
Empire State Development Corp. estimates the legalization of gay marriage will generate about $400 million in economic benefits statewide over three years. The city hopes to be among the biggest benefactors of the law and all the hotel rooms, flowers, dinners out, breakfasts in, and cakes that go with it.
On Monday, the city will host the first group gay wedding in the state for about 50 couples who signed up to tie the knot en masse overlooking Niagara Falls. Officials hope the ceremony will nudge the careworn city perched on one of the world's great natural wonders toward recapturing its storied identity as the world's "Honeymoon Capital."
"We took the honeymoon designation for granted," said Nicholas Mattera, spokesman for the Niagara Tourism & Convention Corp., which has begun redirecting funds and pouring time and manpower into recapturing happy couples of every persuasion. He and other civic leaders acknowledge they've let the blush fade from the Honeymoon Capital reputation over the last three or four decades.
Mayor Paul Dyster had the falls lit up in rainbow hues as he officiated at the city's first same-sex wedding, timed to wrap up at one second past midnight Sunday morning. He gave brides Kitty Lambert and Cheryle Rudd a picture of the illuminated falls as a gift.
Michael Shullick, 31, and Michael McAran, 43, closed up shop at their Sandusky, Ohio, bar at 2:30 a.m. Sunday and drove five hours to Niagara Falls, where they picked up a marriage license for their Monday wedding. They brought along their bar's manager and her girlfriend, who will also wed.
"What more could you ask for, getting married by the falls?"
said Shullick, who said he visited the city a decade or so ago and has wanted to return. Monday's ceremony falls on the couple's three-year anniversary.
Clerks in New York City and about a dozen other cities statewide opened their doors Sunday to cater to same-sex couples.
At the Manhattan clerk's office, a party atmosphere reigned with applause breaking out whenever a couple was handed a white-and-blue wedding certificate. Balloons floated overhead. One couple wore matching kilts; another wore sparkly crowns. Children scurried up and down the lobby; workers with bullhorns called out the numbers of each couple.
Poignant signs of pent-up emotion were common from couples who had in some cases waited for years to wed. Couples cried and voices quavered. Newlywed Douglas Robinson exclaimed, "You bet your life I do!" when asked if he would take Michael Elsasser as his spouse.
The first couple to marry in Manhattan were Phyllis Siegel, 77, and Connie Kopelov, 85, who have been together for 23 years.
Kopelov arrived in a wheelchair and stood with the assistance of a walker. During the service, Siegel wrapped her hand in Kopelov's hand and they both grasped the walker.
Witnesses cheered and wiped away tears after the two women vowed to honor and cherish each other as spouses and then kissed.
"I am breathless. I almost couldn't breathe," Siegel said after the ceremony. "It's mind-boggling. The fact that it's happening to us - that we are finally legal and can do this like everyone else."
Outside afterward, Siegel raised her arms exultantly as Kopelov, in the wheelchair, held out a marriage certificate.
New York's adoption of legal same-sex marriage is viewed as a pivotal moment in the national gay rights movement and was expected to galvanize supporters and opponents alike. The state joined Connecticut, Iowa, Massachusetts, New Hampshire and Vermont, along with Washington, D.C., when it voted to legalize gay marriage.
Opponents in New York say they will seek to block the marriages.
State Sen. Ruben Diaz, a minister who was the sole Democrat to vote against gay marriage, told the crowd at a rally at the United Nations that he and other opponents would try to get Sunday's marriages annulled, saying judges broke the law by waiving the 24-hour waiting period without a good reason.
"We're going to show them next week that everything they did today was illegal," he said, speaking in Spanish. "Today we start the battle! Today we start the war!"
In Manhasset on Long Island, Dina Mazzaferro and Robin Leopold of Great Neck got married in the North Hempstead town clerk's office with their 8-year-old daughter, Sasha, and Robin's mother, Barbara, watching. The elder woman wiped away tears during the brief ceremony while Sasha mouthed some of the words along with her parents.
The couple has been together 15 years.
"We've been waiting for this day," Leopold, an attorney who works in the Queens district attorney's office, said after the service. "And now we're waiting for the day it becomes legal on a federal level. It's a wonderful thing that the town has been so embracing of this."
Across the state in Buffalo, the first in line were Daniel Rodgers, 54, and Scott Klaurens, 40, who were married in shorts, T-shirts and sneakers. They had gone expecting only to get a license and planned to wed Tuesday, but were told they could go ahead Sunday because of their marriage six years ago in Toronto.
"This is just a flower opening up for us and everyone else, a flower of equality," Rodgers said.
At Buffalo City Hall, City Clerk Gerald Chwalinski zipped a black robe over his shorts and golf shirt and spent three hours marrying couples in the ornate City Council chambers. His office issued 20 licenses and performed eight ceremonies in the three hours it was open for the occasion Sunday.
At the end of the day Sunday, the New York City mayor's office said 484 couples had gotten married at city offices while 175 had picked up their licenses in order to marry elsewhere. Most were from the city, but some came from as far as Hawaii and Alabama, officials said.
The festive atmosphere included couples who posed for pictures in front of a photo backdrop of City Hall and bought T-shirts saying "I got married in New York City" from the clerk's office gift shop. In Brooklyn, an elegant reception was held in Borough Hall with champagne and a lineup of cakes - one with a two-men cake topper, another with two women and a third with a heterosexual couple.
At Manhattan's Gracie Mansion, Mayor Michael Bloomberg presided over the wedding of two high-level city officials. Department of Consumer Affairs Commissioner Jonathan Mintz and policy adviser John Feinblatt had been together for 14 years. They were joined by their daughters, ages six and eight, who wore white dresses and held bouquets.
"We're full of love the way other families are," Mintz said.
Associated Press writers George M. Walsh in Albany, Frank Eltman in Manhasset and Verena Dobnik and Samantha Gross in New York City contributed to this report.