Updated

It was held at the home of Red Sox Nation, but the thousands gathered in the seats were there to swear allegiance to an even larger and more powerful nation.

The Oath of Citizenship was taken at Fenway Park by 3,082 immigrants Wednesday as they became the country's newest Americans.

It was the first ever naturalization ceremony at the home of the Green Monster and the World Champion Boston Red Sox, who were in Florida to play the Tampa Bay Rays.

Flanked by the Red Sox's two recent World Championship trophies, Boston Mayor Thomas Menino welcomed the immigrants to their new country. "You all came here because you wanted hope and promises for a better future," he told the crowd.

A quarter of Bostonians were born outside the U.S., Menino said, touting the city's diversity as its strength. "Thank you for choosing America," he said, urging them to register to vote.

The ceremony also commemorated Constitution Week, in honor of the signing of the U.S. Constitution on Sept. 17, 1787.

Thousands more new Americans have been sworn in this year than last. In 2007, 660,000 immigrants were naturalized, Carlos Iturregui, of the U.S. Citizenship and Immigration Services, told the crowd. By the end of this July, 780,000 — including Red Sox slugger David Ortiz, a native of the Dominican Republic — had already taken their oath.

The immigrants who became citizens in Wednesday's ceremony hail from nearly 140 countries. The most — 290 — come from the Dominican Republic, followed closely by China, Haiti, Vietnam and Brazil. About 500 also changed their names as a part of the naturalization process.

Children fidgeted in the stands as their mothers and fathers twirled small American flags.

Massachusetts Army National Guard Spc. Udo Gonzalez, originally from the Dominican Republic, said he had hoped to become an American citizen before he was deployed to Iraq.

"I wanted that flag on the casket," said Gonzalez, a 33-year-old father of five who got back in April.

He sat next to friend Marc Defelice, 36, who moved to the U.S. 18 years ago from Scotland. He's also a specialist in the Massachusetts Army National Guard.

"I just wanted to do something for the country," Defelice said.

Sitting quietly high in the bleachers, Kam Kloeung, 48, said it would be easier to visit relatives in her home country of Cambodia now that she was an American citizen.

She fled to Thailand in 1979, landing in the U.S. two years later, she said. Two of her sisters also escaped and are now living in the U.S.

An older sister was killed under the Khmer Rouge regime, and her parents, brother, and brother-in-law all died from a lack of food and medicine, she said.

In the U.S., she has been a line worker spinning yarn for a fabric maker and has worked in a potato chip factory in South Carolina, but now she stays home in Fall River to care for two grandchildren.

"It's freedom," she said of her new Americanness. "It made me happy."