Unlike some of the other braggadocios, the Wilderness has generally been more reserved with its hyperbole. Even when it could have made claims about its relative size, it allowed other properties to steal its thunder. After it expanded its parks in 2006, however, it began declaring that it was America's largest water park resort.
There's a bit of a snag, however. Unlike most other resorts, which house their parks under one roof, the Wilderness spreads its indoor water parks among three separate buildings. (And the connected, more exclusive Wilderness on the Lake, offers a fourth indoor water park for its guests.) That makes for a lot of barefoot padding through its labyrinth hallways to reach the different parks. The combined square footage of the three main indoor water parks now stands at 250,000 square feet. That makes the Wilderness--TA DA!--America's (and for that matter, North America's) largest indoor water park. But, it is a bit strange that it's not under one roof.
Look out Wilderness. A mega indoor water park resort is under development in Las Vegas that, when and if it opens, would exceed the Wilderness' size.
More Wilderness Water Park Resort Info:
Wilderness Indoor Water Park in Wisconsin Dells Overview