(CNN) — The US is home to more immigrants than any other country — more than 45 million people, according to the latest Census estimates.

That's 13.6 percent of the US population, about the same as it was a century ago. But over the years, we've seen significant shifts in where immigrants to the US come from, and where they end up once they get here.

Here's a look at these key immigration trends and how they've changed over time.

For decades one country has topped the list

Mexicans represent the largest group of immigrants living in the United States. That's been true since 1980, according to the nonpartisan Migration Policy Institute. And the Mexico-US route is the largest migration corridor in the world.

But the total number of Mexican immigrants living in the US has been on the decline for more than a decade.

An estimated 10.7 million Mexican immigrants lived in the US in 2021, roughly 1 million fewer than the number a decade earlier.

Meanwhile, immigration from other countries, including India and China, has been on the rise, according to MPI.

As one expert told CNN last year, the range of reasons why people move to the US from different parts of the world is as varied as the list of countries these immigrants once called home. Some are seeking economic opportunities. Others are fleeing violence, persecution or climate disasters. And others are hoping to reunite with family members who are already here.

According to an analysis of Census data from MPI, the top 10 countries of origin for immigrants in the United States are all in Latin America and Asia.

These statistics include both immigrants who came to the United States legally and those who are living in the country without authorization.

Looking only at the population of undocumented immigrants living in the United States, the list of the top countries of origin shifts slightly. A Department of Homeland Security report in 2021 estimated that the top six countries of origin for undocumented immigrants were Mexico, El Salvador, Guatemala, India, Honduras and China.

But most immigrants who live in the United States aren't undocumented.

The Pew Research Center's latest estimates indicate about 10.5 million undocumented immigrants live in the United States. That means the vast majority of foreign-born people living in the United States (77 percent) are here legally.

Rewinding to the 1960s reveals a different picture

Mexico hasn't always topped the list. Back in 1960, for example, the portrait of US immigrants was dramatically different.

At that time, according to the Migration Policy Institute, the largest group of immigrants were Italians, followed by Germans and Canadians.

Why did things change so significantly? For decades a national original quota system passed by Congress in 1924 favored migrants from northern and western Europe and excluded Asians. In 1965, the Immigration and Nationality Act created a new system that prioritized highly skilled immigrants and those who already had family living in the country. That paved the way for millions of non-European immigrants to come to the United States.

"It fundamentally changed the demographics of the country," Pawan Dhingra, a professor of American Studies at Amherst College, told CNN in 2020.

For decades, the immigrant population in the United States had been decreasing. But the new law also sparked a dramatic increase in immigration in the decades that followed, fueled largely by family reunification.

In 1965, 9.6 million immigrants living in the US comprised just 5 percent of the population, according to the Migration Policy Institute. Now more than 45 million immigrants make up nearly 14 percent of the country.

While the total number of immigrants has reached a historic high, immigrants made up a greater share of the US population in the late 19th and early 20th centuries.

Most states have seen their immigrant populations grow

The makeup of who's coming to the United States isn't the only thing that's changed. There have also been notable shifts in where those immigrants end up.

Arriving immigrants often settled in historic immigrant gateways in major metropolitan areas, such as New York City, Chicago and Boston. But for more than a decade, a much broader swath of locations in the United States have become gateways that are home to growing immigrant populations.

Today, California, Texas, Florida, New York, and New Jersey are home to the largest numbers of immigrants.

But looking at the total number of immigrants in each state only tells part of the story. Some states have larger numbers of immigrants relative to their total populations. In Hawaii, for example, immigrants make up nearly 19 percent of the state's population.

A recent study by the Bush Institute found that many immigrants eventually move from traditional gateway cities to other areas of the country.

"Immigrants making secondary moves within the United States are disproportionately choosing the same places as native-born people — metros with relatively affordable housing and growth-friendly business and tax policies," the study says. "Once there, they gravitate toward fast-growing suburban counties."

For many years, the majority of immigrants lived in the Northeast and Midwest. But now, according to the Pew Research Center's latest analysis, about two-thirds of immigrants live in the West and South.

And in recent years, some states have seen their immigrant populations grow at a faster rate.

As the Bush Institute study notes, job opportunities, affordable housing, family connections and immigrant-friendly policies are among the factors that immigrants consider when deciding where to move.

If current trends continue, experts say in the coming years we could see immigrants make up a historically high share of the US population.

But with geopolitical turmoil around the world and ongoing divisive debates over immigration in Washington, it's hard to predict where future groups of immigrants may come from, or how quickly that milestone will be reached.

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