One by one, they left. And they weren’t coming back. After enjoying many years of sun-splashed swimming in Centennial Park, the people of Wilmette, Ill., began heading elsewhere, to the likes of Skokie, Northbrook, Highland Park and other Chicago suburbs.

The pools“were on the verge of falling apart, really,” says Centennial’s manager, Terry Juliar. “Our residents were going elsewhere to have fun.”

Clearly,action was needed. Commissions were formed, hearings were held. A three-year process ended on June 8, with the gala opening of the Centennial Family Aquatic Center, a waterpark featuring an 11,000-square-foot activity pool with slides and play features, a 50-meter lap pool, a diving well with boards and drop slides, and a zero-depth wading pool.

But it almost didn’t happen.

After all those hearings, the recommendation came back: Build a year-round indoor complex, perfect for snowy Chicago. But residents spoke up — “overwhelmingly,” says Juliar — saying they wanted another outdoor facility, even one open only about three months a year.

Now people have turned their cars around, coming from Glenview, Evanston, Winnetka and Kenilworth to Centennial, located about 20 miles north of Chicago, about three miles from Lake Michigan. The aquatics center, which had about 60,000 patrons last year and never more than 83,000 in Juliar’s 24 years there, surged to 150,000 this past season — and from less than 100 employees to more than 225.

The complex is big news. There was a big story in The Chicago Tribune.

A funny thing happened, however, on the way to the 21st century: The same people who had stopped coming turned sentimental when the aging, 29-year-old facility was closing last year.

“The last two, three days, people came back to reminisce,” Juliar says. “Some of the older people were saying, ‘I had two kids who grew up here. …’

“People were crying. But there were cracks. It was like a sieve. It was time to go.”

But not before longtime members took a little piece of old-time Wilmette with them.

“On the last night, we invited everyone to take a lounge chair home at 9 o’clock,” Juliar says. “It saved us a lot of work, and everyone got a remembrance.”