Nowhere is that wealth more pronounced than Atherton, a longtime billionaire refuge that’s now seeing resurgent real estate demand. AdvertisementWith the boom, Atherton has regained the title of the most expensive U.S. ZIP Code, surpassing Miami’s Fisher Island, according to PropertyShark. The top 1% of priciest homes in the U.S. start just under $5.5 million, according to Realtor.com. Privacy fears are also pushing more of Atherton’s ultra-luxury real estate market to the shadows. Last year, about 24% of homes in Atherton sold off public listings, up from 21% a year prior, according to Cornish.