DALLAS — The mural painted on the side of a building in the Deep Ellum warehouse district here is intentionally vague, simply showing a faceless man in a suit holding an umbrella over the words “Life in Deep Ellum.” Inside there are the trappings of a revitalization project, including an art gallery, a yoga studio and a business incubator, sharing the building with a coffee shop and a performance space.

But it is, in fact, a church.

Life in Deep Ellum is part of a wave of experimentation around the country by evangelicals to reinvent “church” in an increasingly secular culture, and it comes as the megachurch boom of recent decades, with stadium seating for huge crowds, Jumbotrons and smoke machines, faces strong headwinds. A national decline in church attendance, the struggling economy and the challenges of marketing to millennials have all led to the need for new approaches.

“It’s unsettling for a movement that’s lasted 2,000 years to now find that, ‘Oh, some of the things we always assumed would connect with the community aren’t connecting with everyone in the community in the way they used to,’ ” said Warren Bird, the director of research for the Leadership Network, a firm that tracks church trends.

According to a recent report by the Pew Research Center, the percentage of Americans who are not affiliated with any religion is on the rise, including a third of Americans under 30. Even so, 68 percent of unaffiliated Americans say they believe in God, and 41 percent say they pray at least once a month.