Chicago is a city in Northeastern Illinois. It is the largest city in the state, and the third-largest in the United States, with 2.7 million residents. It's among the top five most economically powerful cities in the world, according to Forbes.

The Heroes of Olympus

The Lost Hero

Leo Valdez, Piper McLean, and Jason Grace visit the city during their Quest to Free Hera. They go to an underground mall owned by Medea, a servant of Gaea. Piper defeated Medea by combining potions that caused the mall to explode. Jason, Piper, and Leo escape on Festus.

Locations (CHB)
Magical Locations: Aeolia | Camp Half-Blood (Grove of Dodona) | Camp Jupiter | Cave of Trophonius | C.C.'s Spa and Resort | Daedalus' Workshop | Lotus Hotel and Casino | Mount Othrys | Ogygia | Olympus | Pan's Cave | Sea of Monsters | The Labyrinth | Tartarus | Underworld | Waystation
Cities, States, and Towns: Alaska | Bar Harbor | Bologna | Chicago | Detroit | Gila Claw | Indianapolis | Jamestown | Long Island | New York City (Manhattan) | Quebec | San Francisco | Dalmatia (Split) | Vancouver | Venice | Westport
Other Locations: Apennine Mountains | Aunty Em's Gnome Emporium | Carlsbad Caverns | Crusty's Water Bed Palace | Empire State Building | Gateway Arch | Grand Canyon | Greece | Hoover Dam | Italy | Junkyard of the Gods | Mount Diablo | Mount Etna | Mount Saint Helens | Mount Tamalpais | Pikes Peak | Polyphemus' Island | ROFL | Rome | Triple G Ranch | U.S.A. | Waterland