MANKATO — Sidney and Mitch Elofson were top-flight tennis players in St. Peter, Minn., where they grew up, and at Gustavus Adolphus College, where they went to college.

But they're making a multimillion-dollar bet on another sport: pickleball, a sort of cross between tennis and ping-pong that's taking the nation by storm. More than 4.2 million Americans play the paddle sport, a jump of more than 20% in just the past year. Locally, the Mankato Area Pickleball Association has more than 250 members, less than a decade after the group was started by about a dozen people.

It's so popular that even the nuns of the School Sisters of Notre Dame play it on their Mankato campus.

The Elofsons looked at all that and saw an opportunity. They started planning two years ago, and now their dream is taking shape on 8 acres in northeast Mankato. There, construction is underway on the Picklebarn, an indoor pickleball complex that will make Mankato "the mecca of pickleball in southern Minnesota and northern Iowa," according to John Sandry, the local association's president. The 27,000-square-foot facility, with eight indoor courts, is expected to open in late spring.

It's a leap of faith for the couple, both 28, who haven't run a business before. But they see a bright future for the sport, which promoters tout as a family-friendly game that's accessible to all ages and skill levels.

"A grandparent can play with a grandchild," Sidney Elofson said. "It's a real family sport."

Both the Elofsons recently quit their jobs — Mitch as a tennis coach, Sidney as a strength and conditioning coach — to get the Picklebarn going. After a feasibility study, they secured a Small Business Administration loan through Profinium Bank for a sum they described as "multimillion."

"I thought I would faint when we kept signing the loan documents," Sidney Elofson said with a laugh. But normal jitters aside, the couple is confident that their venture will succeed.

"It's such an accessible sport to all ages, skill levels and generations," Mitch Elofson said. "People just want to get together and have fun and make memories," Sandry agrees.

"Every year it's growing," he said. Sandry discovered pickleball in Arizona, where he's a snowbird.

"I tried it, and it was hook, line and sinker," he said. His wife, Joyce, said she's living proof of how easy it is to learn the game.

"I've never played any sport at any level in my life, and I can play pickleball," she said.

According to USA Pickleball, the game was invented in the 1960s in the Pacific Northwest, an area where competitive rowing is popular. When there are extra rowers without an assigned boat, they get tossed together into a makeshift crew called the "pickle boat."

Since the inventors of the game used odds and ends of sporting goods they had on hand, they named it after the thrown-together crews.

The Picklebarn eventually will add outdoor pickleball courts, along with clay tennis courts. Courts will be available for rental by the hour, or players can buy memberships that will confer added benefits. The barn also will host league play and tournaments, along with classes.

The building will include a 4,000-square-foot mezzanine where guests can watch and socialize or hold corporate events. The Elofsons plan to have a liquor license and partner with local businesses on food for the facility.

"It's been very exciting to pursue the dream," Mitch Elofson said. "Also very scary and challenging."