Lisa Tofano was baptized, confirmed and married at the Good Shepherd Lutheran Church on Lake Opeka in Des Plaines, Ill. When she and her husband, John, visited the church last fall, however, it wasn’t to worship but rather to celebrate their 34th wedding anniversary at what the church had become: the Foxtail on the Lake, a restaurant.

The transformation was not easy: The shuttered church needed an 18-month, $6 million gut renovation, and a new 3,000-square-foot kitchen, before it could start offering items like paella and beef shawarma, said David Villegas, a managing partner of Foxtail, who said he had been “a bit nervous” before the restaurant’s opening in November about the reaction of former parishioners. For Mrs. Tofano, though, “a church is more about the people than the building,” she said.

Across the country, the number of empty churches and other houses of worship is sharply rising, and these structures, often unique architectural gems, have become huge draws for business owners.

Eileen Lindner, a sociologist and Presbyterian minister who is a former editor of the Yearbook of American & Canadian Churches, which analyzes census data on religious organizations and houses of worship, said that she expected as many as 100,000 Protestant church properties to close by 2030. That figure, which may come close to 20 percent of all existing Protestant churches, is a significant increase over the past decade, Ms. Lindner said.

Lisa Tofano, a former parishioner at Good Shepherd, was married there 34 years ago.Credit…via Lisa Tofano

The closings stem largely from a drop in church attendance during the Covid pandemic, and fewer people, especially younger adults, affiliated with religious organizations than in the past. The decline has been happening for decades. In the late 1940s, 76 percent of Americans said they belonged to a church, synagogue or mosque, but by 2020 that number had dropped to 47 percent, Gallup polling found.