Oak Brook is a village in DuPage County, Illinois, with a very small portion in Cook County. The population was 8,163 at the 2020 census. A suburb of Chicago, it contains the headquarters of Ace Hardware, Portillo's Restaurants, Blistex, Federal Signal, CenterPoint Properties, Sanford L.P., TreeHouse Foods, Lions Clubs International, U.S. Census Bureau Chicago regional office, and former headquarters of McDonald's and Ferrara Candy. The Lizzadro Museum of Lapidary Art moved here in 2019.