Agua Negra, Mexico — The extraordinary Mexican migration that delivered millions of illegal immigrants to the United States over the past 30 years has sputtered to a trickle, and research points to a surprising cause: unheralded changes in Mexico that have made staying home more attractive.

A growing body of evidence suggests that a mix of developments — expanding economic and educational opportunities, rising border crime and shrinking families — are suppressing illegal traffic as much as economic slowdowns or immigrant crackdowns in the United States.

Here in the red-earth highlands of Jalisco, one of Mexico’s top three states for emigration over the past century, a new dynamic has emerged. For a typical rural family like the Orozcos, heading to El Norte without papers is no longer an inevitable rite of passage. Instead, their homes are filling up with returning relatives; older brothers who once crossed illegally are awaiting visas; and the youngest Orozcos are staying put.

“I’m not going to go to the States because I’m more concerned with my studies,” said Angel Orozco, 18. Indeed, at the new technological institute where he is earning a degree in industrial engineering, all the students in a recent class said they were better educated than their parents — and that they planned to stay in Mexico rather than go to the United States.

Douglas S. Massey, co-director of the Mexican Migration Project at Princeton, an extensive, long-term survey in Mexican emigration hubs, said his research showed that interest in heading to the United States for the first time had fallen to its lowest level since at least the 1950s. “No one wants to hear it, but the flow has already stopped,” Mr. Massey said, referring to illegal traffic. “For the first time in 60 years, the net traffic has gone to zero and is probably a little bit negative.”

The decline in illegal immigration, from a country responsible for roughly 6 of every 10 illegal immigrants in the United States, is stark. The Mexican census recently discovered four million more people in Mexico than had been projected, which officials attributed to a sharp decline in emigration.

American census figures analyzed by the nonpartisan Pew Hispanic Center also show that the illegal Mexican population in the United States has shrunk and that fewer than 100,000 illegal border-crossers and visa-violators from Mexico settled in the United States in 2010, down from about 525,000 annually from 2000 to 2004. Although some advocates for more limited immigration argue that the Pew studies offer estimates that do not include short-term migrants, most experts agree that far fewer illegal immigrants have been arriving in recent years.

The question is why. Experts and American politicians from both parties have generally looked inward, arguing about the success or failure of the buildup of border enforcement and tougher laws limiting illegal immigrants’ rights — like those recently passed in Alabama and Arizona. Deportations have reached record highs as total border apprehensions and apprehensions of Mexicans have fallen by more than 70 percent since 2000.

But Mexican immigration has always been defined by both the push (from Mexico) and the pull (of the United States). The decision to leave home involves a comparison, a wrenching cost-benefit analysis, and just as a Mexican baby boom and economic crises kicked off the emigration waves in the 1980s and ’90s, research now shows that the easing of demographic and economic pressures is helping keep departures in check.

In simple terms, Mexican families are smaller than they had once been. The pool of likely migrants is shrinking. Despite the dominance of the Roman Catholic Church in Mexico, birth control efforts have pushed down the fertility rate to about 2 children per woman from 6.8 in 1970, according to government figures. So while Mexico added about one million new potential job seekers annually in the 1990s, since 2007 that figure has fallen to an average of 800,000, according to government birth records. By 2030, it is expected to drop to 300,000.

Even in larger families like the Orozcos’ — Angel is the 9th of 10 children — the migration calculation has changed. Crossing “mojado,” wet or illegally, has become more expensive and more dangerous, particularly with drug cartels dominating the border.

At the same time, educational and employment opportunities have greatly expanded in Mexico. Per capita gross domestic product and family income have each jumped more than 45 percent since 2000, according to one prominent economist, Roberto Newell. Despite all the depictions of Mexico as “nearly a failed state,” he argued, “the conventional wisdom is wrong.”

A significant expansion of legal immigration — aided by American consular officials — is also under way. Congress may be debating immigration reform, but in Mexico, visas without a Congressionally mandated cap on how many people can enter have increased from 2006 to 2010, compared with the previous five years.

State Department figures show that Mexicans who have become American citizens have legally brought in 64 percent more immediate relatives, 220,500 from 2006 through 2010, compared with the figures for the previous five years. Tourist visas are also being granted at higher rates of around 89 percent, up from 67 percent, while American farmers have legally hired 75 percent more temporary workers since 2006.

Edward McKeon, the top American official for consular affairs in Mexico, said he had focused on making legal passage to the United States easier in an effort to prevent people from giving up and going illegally. He has even helped those who were previously illegal overcome bans on entering the United States.

“If people are trying to do the right thing,” Mr. McKeon said, “we need to send the signal that we’ll reward them.”

Hard Years in Jalisco

When Angel Orozco’s grandfather considered leaving Mexico in the 1920s, his family said, he wrestled with one elemental question: Will it be worth it?

At that point and for decades to come, yes was the obvious answer. In the 1920s and ’30s — when Paul S. Taylor came to Jalisco from California for his landmark study of Mexican emigration — Mexico’s central highlands promised little more than hard living. Jobs were scarce and paid poorly. Barely one of three adults could read. Families of 10, 12 and even 20 were common, and most children did not attend school.

Comparatively, the United States looked like a dreamland of technology and riches: Mr. Taylor found that the wages paid by the railroads, where most early migrants found legal work, were five times what could be earned on farms in Arandas, the municipality that includes Agua Negra.

Orozco family members still talk about the benefits of that first trip. Part of the land the extended family occupies today was purchased with American earnings from the 1920s. When Angel’s father, Antonio, went north to pick cotton in the 1950s and ’60s with the Bracero temporary worker program, which accepted more than 400,000 laborers a year at its peak, working in the United States made even more sense. The difference in wages had reached 10 to 1. Arandas was still dirt poor.

Antonio, with just a few years of schooling, was one of many who felt that with a back as strong as a wooden church door, he could best serve his family from across the border.

“I sent my father money so he could build his house,” Antonio said.

Legal status then meant little. After the Bracero program ended in 1964, Antonio said, he crossed back and forth several times without documentation. Passage was cheap. Work lasting for a few months or a year was always plentiful. So when his seven sons started to become adults in the 1990s, he encouraged them to go north as well. Around 2001, he and two of his sons were all in the United States working — part of what is now recognized as one of the largest immigration waves in American history.

But even then, illegal immigration was becoming less attractive. In the mid-1990s, the Clinton administration added fences and federal agents to what were then the main crossing corridors beyond Tijuana and Ciudad Juárez. The enforcement push, continued by President George W. Bush and President Obama, helped drive up smuggling prices from around $700 in the late 1980s to nearly $2,000 a decade later, and the costs continued to climb, according to research from the Center for Comparative Immigration Studies at the University of California, San Diego. It also shifted traffic to more dangerous desert areas near Arizona.

Antonio said the risks hit home when his nephew Alejandro disappeared in the Sonoran Desert around 2002. A father of one and with a pregnant wife, Alejandro had been promised work by a friend. It took years for the authorities to find his body in the arid brush south of Tucson. Even now, no one knows how he died.

But for the Orozcos, border enforcement was not the major deterrent. Andrés Orozco, 28, a middle son who first crossed illegally in 2000, said that while rising smuggling costs and border crime were worries, there were always ways to avoid American agents. In fact, while the likelihood of apprehension has increased in recent years, 92 to 98 percent of those who try to cross eventually succeed, according to research by Wayne A. Cornelius and his colleagues at the University of California, San Diego.