TIJUANA, Mexico —They come for the tacos. Or the music. Or the nightlife.

They stay to live a less-expensive lifestyle or to retire in a casita in the sand.

Americans immigrants living the Mexican dream can have the same hopes and goals of the Mexican immigrant in the United States: to get a little ahead or to start a new life.

There may be more Americans living south-of-the-border than previously noticed.

Last month, Mexico’s President Andres Manuel Lopez Obrador tasked his foreign minister, Marcelo Ebrard, with gathering data on U.S. immigrants, who also go largely undocumented.

The Mexican government determined Americans are actually Mexico’s largest group of immigrants.

Lopez Obrador mentioned the southbound surge last week during a speech in Tijuana promoting friendship between the two countries.

“A little-cited fact is that in Mexico, there are about 1.2 million Americans. That is, our two countries are protagonists of the largest demographic exchange in the world,” said Lopez Obrador.

The U.S. Embassy in Mexico City said the figure might be an undercount, because many Americans overstay their visa.

They estimated there are more than 1.5 million U.S.-born citizens in Mexico, including some 600,000 U.S.-born children of Mexican parents whose families have returned home.

For 34-year-old Josh Nichols, who moved to Mexico City three years ago and now lives in Tijuana, it wasn’t the cheaper rent or the nightlife or the beaches.

He fell in love with the culture and the pace of his lifestyle south of the border.

“(Here) I probably get to spend a lot more of my time just socializing, especially with people that I don’t know,” said Nichols. “One of the things I really like about Mexico is just that people tend to be more open.”

Nichols mentioned the Spanish word convivencia, which translates to coexistence, but he said he doesn’t think the translation gives the full context of the word.

“You know how the Eskimos have so many different words for snow? If you interact with something more, you have more vocabulary to describe that thing,” he said. “I don’t know that we have a word in the United States for just sharing time with one another and I think that word reflects a big cultural difference between the two countries.”

The number of Americans living in Mexico has increased by more than four times since 1990, according to federal data.

In Mexico, the federal government takes a very different approach with its American immigrant population, whether they are legal or not.

“We have never pressured them to have their documents in order,” Mexico’s Foreign Minister Marcelo Ebrard told The Washington Post.

He has not yet respond to questions from the Union-Tribune about whether that lenient attitude will continue amid Mexico’s crackdown on migration spurred by pressure from the Trump administration. But that’s unlikely. Mexican authorities believe Americans stimulate the local economy, just like Mexicans do in the U.S., they said.

If and when the Mexican government does enforce their immigration laws against Americans who overstay their six-month visa, it’s usually just with a small fine.

But “expats,” as they call themselves, could face other penalties.

International tax attorney Enrique Hernandez-Pulido said U.S. citizens living in Mexico may face tax obligations they are unaware of, which could result in a costly fine.

“The first thing to understand is that the U.S. is the only country in the world that taxes based on citizenship and not residency,” said Hernandez-Pulido.

That means a U.S. citizen living in Mexico, even if they work for a Mexican company, has to pay taxes to the U.S. on that income.

“What happens is many people, maybe the majority, have tax obligations in the U.S. that they may not know about and may not be paying or complying with,” he said.

Hernandez-Pulido said often times people living in Mexico earning under a certain amount will only have to file for an exemption with the IRS, but if they don’t do it, they could face the $10,000 tax fine.

“So, let’s say you have a retiree down in San Felipe with $15,000 in the bank collecting a small amount of interest annually. They probably don’t owe much, but if they don’t file for that exemption, it can become a nightmare for them,” he said, who feels bad for U.S. retirees who have faced stiff penalties during a U.S. crackdown on collecting those fines.

“They just go to live a simpler life, stretch out their retirement dollars, but they can end up with a ‘tax tragedy’ that almost cleans them out,” Hernandez-Pulido said.