Pope Francis on Tuesday stepped onto U.S. soil for the first time, beginning a jam-packed six-day tour that includes a meeting with President Obama at the White House, an address to a joint session of Congress, and brief visits to New York and Philadelphia.

Wherever the Pope goes, hundreds of thousands of ecstatic, adoring followers will be waiting to catch a glimpse.

And that begs the question, who are America's Catholics today?

A 2014 Pew Research study on U.S. religious demographics found that although the number of Catholics in America had declined by about three million followers since its last survey in 2007, Catholics remain one of the largest religious groups in the country (second only to Evangelical Protestants) . According to the study, about one in five American adults -- roughly 51 million people -- say their primary religious affiliation is with the Catholic Church.

Nearly a third of the U.S. House of Representatives is Catholic. Almost evenly divided between Republicans and Democrats, these 137 members include Majority Leader John Boehner (R-OH) and Minority Leader Nancy Pelosi (D-CA). Meanwhile, 26 members of the Senate -- just over a quarter -- are Catholic.

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It also found that today's U.S. Catholic population has grown increasingly diverse: Catholics are now more likely than other Americans to be immigrants or children of immigrants, many of whom are Hispanic. In fact, more than a quarter (27 percent) of U.S. Catholic adults today were born outside of the U.S., compared to 15 percent of U.S. adults overall.

It also found notable geographic shifts, with the share of Catholics declining slightly in the Northeast and Midwest but increasing in parts of the South and West. In 2014, 28 percent of adults in California identified as Catholic, including 25 percent in the San Francisco metro area.

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