Estimated home value: $116.2 million
Title: Cofounder, Microsoft; Chairman, Vulcan
Seattle native Allen owns homes in Manhattan, Atherton, Malibu, Beverly Hills, Hawaii, London, and St. Jean Cap-Ferrat, France, but none are as impressive as his estate on Mercer Island, Washington, close to where he grew up. Nine structures spread across 11 parcels of land add up to a value of $116.2 million, according to the King County public assessor's office.
While Allen mainly occupies one of them, one is occupied by his mother, and many others serve as guest homes to friends and celebrities alike (he has never been married and has no children). The homes come with some pretty fantastic features, including a floating helipad, an NBA-regulation-size basketball court, an enormous fitness center, a ballroom, a gorgeous swimming pool with a water slide, and thousands of square feet of water frontage.