By Jim Spellman, CNN

Denver (CNN) - Kristen Kelly was raised Roman Catholic, attended Catholic elementary school and considered herself a good Catholic, but when she was 21-years-old that changed.

“A coworker asked me if I believe in Jesus Christ,” she says.

Despite spending her entire life in the Roman Catholic Church she couldn’t answer the question.

“I never really got exposed to Christ," she says. "It was more about Mary and the Church and a condemnation of everything I was doing wrong.”

She looked at her coworker and saw someone who appeared to have a personal relationship with Jesus Christ and decided that was what she wanted. She said this prayer:

“Jesus I accept that you are my lord and savior, and I ask you to come into my life.”

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And from that moment Kelly, now 41 and living in Florida, considered herself born-again, and an ex-Catholic.

“I like to call us recovering Catholics,” she says with a laugh.

According to a 2008 study by the Pew Forum on Religious Life and Public Life, 31% of Americans were raised Catholic, but only 24% now describe themselves as Catholic. Read the study (PDF).

That means about 1 in 10 Americans is an ex-Catholic. If they were a denomination they would be bigger than Methodists, Baptists, Lutherans and Presbyterians.

The total U.S. Catholic population has remained at about 24%, as immigrants have filled the pews the ex-Catholics have left behind.

Video: Why do some Catholic outsiders remain inside the flock?

Kathleen Cummings , associate director at the Cushwa Center for the Study of American Catholicism at Notre Dame, says that some people leave the Catholic Church after a defining event like the priest abuse scandals or because of a disagreement with the Church over social issues, but most leave because they feel their needs are not being met.

“They are not experiencing something that fulfills them spiritually,” Cummings says.

Church supporters are urging wayward Catholics to return to the fold. For example, Catholics Come Home, a nonprofit lay organization formed in 1997, has been putting out the welcome mat via the media.

The group has an interactive website www.Catholicscomehome.org and airs what it calls “evangomercials” on radio and television. The group says that since 2008 more than 350,000 people have “come home” to the Catholic Church through their campaign.

Tom Peterson, president of Catholics Come Home, says some worshipers who've returned to the Catholic Church report leaving because they had disagreements with church officials or had divorced and feared they wouldn’t be welcome. But, he says, the majority never really gave up on the Church.

“They just drifted away and life got too busy," Peterson says. "Most say they didn’t dislike the Church, nor were they opposed to the Church teachings.

“An overwhelming majority of returnees tell our diocesan partners that they came home to the Catholic Church, 'because you invited me,'" he says.

But it may not be so simple to lure back ex-Catholics like Matt Rowe, a 35-year-old married father of two living in Denver. Rowe attended 16 years of Catholic School in Illinois and attended a Catholic university.

But by the end of college, Rowe was adrift. He found himself disagreeing with the Church on everything from the role of women to the concept of original sin and what he saw as the Catholic Church’s dependence on guilt as a motivating factor.

Rowe gave up on religion for most of his 20s but never stopped believing in God. When he got married and had kids, he started feeling a void in his life.

“I wanted my kids to grow up in a religion, but not Catholicism,” he says.

After “church-hopping” for a few years, Rowe ended up at Pathways Wash Park, a multidenominational Christian church in Denver.

After years of feeling disconnected in the Catholic Church where he says sermons rarely connected to his life, he has finally found the connection he has been looking for at Pathways.

“I wanted spirituality. I wanted God. I wanted all those points to go back to what I’m dealing with today,” Rowe says.

Fred Viarrial, 59, grew up as an altar boy at St. Leo’s in Denver. Six days a week he donned his cassock and worked the 6 a.m. Mass.

“Books or bells. You are ringing the bells or moving the books for the priests,” Viarrial says.

But as he grew up he began questioning elements of Catholicism. One day, when Viarrial was somewhere between age 10 and 12, he had something especially embarrassing to confess, so he trekked over to a Spanish language parish where he was unknown.

“The priest pulled me out and spanked me on the spot,” Viarrial says with a laugh. “That got me to question this whole thing of confession.”

When he was just 14 the precocious teenager went so far as to schedule an appointment with Denver ‘s then-Archbishop James Casey to discuss his doubts.

“I took a two-page list of questions starting with the Hail Mary. I wanted to find them in the Bible, their origin … where is that in the Bible?”

Viarrial says the archbishop humored him but ultimately did not answer his questions.

He still believed in God, but was losing faith in the Church.

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By his 20s he was searching for a new church and ended up at Arvada Covenant Church, an evangelical congregation in a Denver suburb.

At Arvada Covenant he says the focus is on a personal relationship with Jesus and that his questions about his faith and the Bible are not met with derision, but with a search for answers through Bible study.

He has found a home at Arvada Covenant, but says he holds no grudge against the Catholic Church and still feels echoes of his Catholic upbringing in his faith today.

“It’s like a spiritual tattoo that you receive as a kid," Viarrial says. "Those roots don’t ever disappear, you just better try to understand them.”