At Rooftop Church, located just outside the vibrant city of St. Louis, Missouri, the traditional attire of clerical collars and frocks is replaced with a more casual wardrobe of baseball caps and jeans. This relaxed atmosphere is set by head pastor Matt Herndon, who leads the congregation every Sunday.

“When people first walk in, they’re often surprised by things they don’t typically see in other churches,” Herndon explains. “For instance, they might notice I’m wearing a hat, or we might show a clip from ‘Beauty and the Beast’ during the service. Our goal is to engage with people in a way that’s relatable and understandable for them.”

Rooftop Church is among approximately 40,000 nondenominational Christian churches across the United States. These churches base their teachings on the Bible while maintaining independence from specific denominations. What Herndon started nearly 25 years ago in a community center has grown into a thriving congregation, drawing as many as 600 attendees each week.

Ryan Burge, a professor specializing in the influence of religion on American life at Washington University, notes, “Nondenominational churches are now the most powerful force in American Christianity. They emphasize a personal relationship with Jesus Christ. Many of these churches preach a conservative gospel on issues like abortion and same-sex marriage, but they don’t prioritize these topics in their messages.”

“Nondenominational is actually the strongest force in American Christianity right now,” said Ryan Burge, a professor who focuses on religion’s impact on American life at Washington University. “They really talk about a personal relationship with Jesus Christ. Many of them preach a conservative gospel on things like abortion, same sex marriage, but they don’t lead with those things.”

In 1972, fewer than 3% of Americans identified as nondenominational Christians. Now it’s 14% or nearly 40 million people, according to the General Social Survey.

Burge believes it’s possible nondenominational Christians could overtake Roman Catholics in the next 15 years to be “the largest religious tradition in America.”

“I think it’s, we’re moving away from authority structure,” Burge said.

That looser structure is what attracts Rooftop members Anna and Nathan King, who grew up attending traditional Christian churches.

“Here at Rooftop, we focus on thinking critically about those traditions and challenging each other, but not letting it divide us,” Anna said.

“I love how casual it is. It’s really cool that, like, we could be in the pews and one of our elders or pastors is right in the pew next to us,” Nathan said.

Herndon calls this “big tent Christianity.” He uses videos and pop culture while focusing on what he sees as the fundamentals of the bible, without taking a hard line.

When asked what he would say to people who view his church as “Christianity light,” Herndon said, “I emphatically disagree. We dig really deep into scripture, we just try to figure out, what does this mean for people?”

He added, “Some denominations, more traditional denominations, I think they’ve realized, we don’t have much of a future unless we try to figure out how to reconnect with people.”