this article uses some info from Watch Dogs wiki
Willis Tower is a skyscraper in Chicago.
The Willis Tower is the second tallest skyscraper in the United States, and the tallest skyscraper in Chicago. It is located at 233 South Wacker Drive, in The Loop district. The skyscraper has an accessible interior, and Aiden Pearce is able to enter the building's lobby.
Most notably suffering from hacking in 11 years, since the WTC collapses. This is due to the antenna on the building's roof. Which when hacked leads to the Chicago, and the country's most secrets. That are acessed through Wi-Fi.