WASHINGTON — New census data released today affirm a clear and sustained drop in illegal immigration, ending more than a decade of increases.

The number of illegal immigrants in the U.S. dropped to an estimated 11.1 million last year from a peak of 12 million in 2007, part of an overall waning of Hispanic immigration. For the first time since 1910, Hispanic immigration last year was topped by immigrants from Asia.

Demographers say illegal Hispanic immigration — 80 percent of all illegal immigration comes from Mexico and Latin America — isn’t likely to approach its mid-2000 peak again, due in part to a weakened U.S. economy and stronger enforcement but also a graying of the Mexican population.

The finding suggests an uphill battle for the Republicans, who passed legislation in the House last week that would extend citizenship to a limited pool of foreign students with advanced degrees but who are sharply divided on whether to pursue broader immigration measures.

In all, the biggest surge of immigration in modern U.S. history ultimately may be recorded as occurring in the mid-1990s to early 2000s, yielding illegal residents who now have been settled in the U.S. for 10 years or more. They include migrants who arrived here as teens and are increasingly at risk of “aging out” of congressional proposals such as the DREAM Act that offer a pathway to citizenship for younger adults.

“The priority now is to push a vigorous debate about the undocumented people already here,” said Jose Antonio Vargas, 31, a journalist from the Philippines. “We want to become citizens and not face the threat of deportation or be treated as second class,” said Vargas, whose campaign, Define American, along with the young immigrant group United We Dream, have been pushing for citizenship for the entire illegal population in the U.S. The groups point to a strong Latino and Asian-American turnout for President Barack Obama in last month’s election as evidence of public support for a broad overhaul of U.S. immigration laws.

Earlier this year, Obama extended to many younger immigrants temporary reprieves from deportation. But Vargas, who has lived in the U.S. since 1993 and appeared this year on the cover of Time magazine with other immigrants who lacked legal status, has become too old to qualify.

“This conversation is a question about how we as a nation define who is an American,” Vargas said, noting that if politicians don’t embrace immigration overhaul now, a rapidly growing bloc of minority voters may soon do it for them. “If you want us to pay a fine to become a citizen, OK. If you want us to pay back taxes, absolutely. If you want us to speak English, I speak English. But we can’t tread water on this issue anymore.”