Pope Francis will arrive Sept. 22 in the United States to find a Catholic church playing a prominent role in American life, with a vast network of charities and an infusion of energy from a fast-growing Latino population. At the same time, the church is struggling to find its footing a few months after gay marriage became legal and as more people leave organized religion behind.

Here are some key things to know about the Roman Catholic Church in the United States:

BIG NUMBERS: The Catholic Church is by far the largest denomination in the U.S., with more than 68 million parishioners. By comparison, the next-biggest faith group, the Southern Baptist Convention, counts 15.5 million members. About one-quarter of Americans identify as Catholic.

LATINO BOOM: Through immigration and high birth rates, Latinos now make up 38 percent of the U.S. church. The Archdiocese of Los Angeles, the nation's largest diocese, is about 70 percent Latino; the Archdiocese of Atlanta is 44 percent. Yet, Latinos aren't sticking with the church the way they once did. More are leaving for evangelical Protestant groups or dropping organized religion altogether.

EX-CATHOLICS: Despite the church's large size, it has been posting significant losses. In a recent poll by the Pew Research Center, 9 percent of Americans said they were raised Catholic but were no longer part of the faith in any way. Another group, often dubbed "cultural Catholics," identify with the faith but almost never step foot in a church. Since 1977, weekly Mass attendance has dropped from 41 percent to 24 percent of adult Catholics. Bishops have taken to running campaigns, such as the Archdiocese of Washington's "The Light Is On For You," to persuade Catholics to take part in the sacrament of confession.

GO WEST: The center of gravity for the church is shifting from the older Catholic strongholds of the Northeast and Midwest to the burgeoning South and West. The Archdiocese of New York, which Francis will visit on this trip, is closing or merging nearly one-third of its parishes. The prominent Archdiocese of Chicago posted the fourth-highest losses of any diocese nationwide over the last decade. Meanwhile, the Archdiocese of Galveston-Houston in Texas grew the most, adding more than 667,000 parishioners, according to the Center for Applied Research at Georgetown University.

PRIEST SHORTAGE: As in many countries, the U.S. church is suffering from a shortage of priests. In 1965, nearly 59,000 priests served in the church. That number has dropped below 38,000. About 3,500 of the more than 17,000 parishes don't have a resident priest. And with 40 percent of U.S. priests over age 65, dioceses are bracing for a wave of retirements that could leave even more pulpits empty.

ABUSE SCANDAL: The American church is still dealing with the clergy sex abuse scandal, which erupted in 2002 with the case of one pedophile priest in the Archdiocese of Boston, then spread nationwide and beyond. Three dioceses — Gallup, New Mexico, Milwaukee, and St. Paul and Minneapolis — are in bankruptcy court, trying to limit payouts to victims and preserve church assets. The Archdiocese of St. Paul and Minneapolis is being prosecuted on charges of failing to protect children. And the Diocese of Honolulu is facing a raft of new claims after lawmakers temporarily lifted time limits on lawsuits. Just this year, Bishop Robert Finn in Kansas City-St. Joseph, Missouri, and Archbishop John Nienstedt in St. Paul and Minneapolis stepped down after improperly handling abuse cases. The overall costs of the crisis — for settlements, attorneys and child safeguards in dioceses — is in the billions of dollars.

FINANCES: The U.S. Catholic church is one of the wealthiest in the world — and one of the biggest donors to the Vatican. Yet, individual dioceses and parishes are struggling, in part because Catholics don't donate at high rates to their parishes, according to the Center for Church Management & Business Ethics at Villanova University. In 2013, nearly one-third of Catholic parishes operated at a loss. Church jobs once filled by volunteers and nuns now require paid staff. Pension plans for clergy are underfunded by tens of millions of dollars and property maintenance costs are rising. Nearly a third of church buildings across the country are more than 80 years old. The costs of the abuse scandal have added to the strain. A dozen U.S. dioceses sought bankruptcy protection from abuse claims.

CHARITY: The Catholic church, through its nationwide network of charities, schools and hospitals, is one of the largest social service providers in the country. Catholic Charities USA, a more than $4 billion a year agency, helps the poor and homeless, provides adoption services and resettles immigrants and refugees. Catholic Relief Services, the bishops' international humanitarian arm, is a major force in development and disaster relief overseas. (Both agencies receive significant government grants.) Dioceses also run their own local programs. The Archdiocese of Philadelphia, which Francis will visit, spends more than $4 million each year on services to the poor, homeless and disabled, while managing about $100 million in government funds for similar work, Archbishop Charles Chaput said.

SOURCES: Center for Applied Research in the Apostolate at Georgetown University; Pew Research Center; Center for Church Management & Business Ethics at Villanova University.