Chicago was a city in the state of Illinois in the United States on Earth. It was home to many notorious gangsters in the 1920s, who took advantage of the prohibition of alcohol by selling it through illegal speakeasies. During that time, the Seventh Doctor and Ace went to Chicago, where they met Al Capone and Tom Dekker. (PROSE: Blood Harvest)
In 1883, Valarie Lockwood and Roanna both arrived in Chicago. Roanna promptly fell victim to a virus called the Surge, transforming into an energy-hungry mutant. Valarie, having met Hayden Lockwood during an adventure at the World's Fair ten years hence, sought him out for help, and together, they subdued and captured Roanna. Over the following decade, they established and built up the Lockwood Foundation, an organization dedicated to solving the mystery of the Surge, fell in love, and married. (AUDIO: All's Fair)
In 1893, the younger Valarie and Roanna went on a date to the World's Fair. After a demonstration of electric lighting which was received rather tepidly, they were approached by Hayden, claiming to be Valarie's husband. The couple reacted as expected for a duo clueless to their futures, though they did bring him to the TARDIS to meet the Eleventh Doctor. While they returned to the Fair to ride the world's first Ferris wheel, the Doctor and Hayden visited the Lockwood Foundation, where Hayden introduced the Doctor to their work involving the Surge.
Frank Garcia, an employee at the Foundation, attempted to assassinate Roanna before she could mutate. Failing in this, he succumbed to the Surge himself, attacking Valarie and Roanna in search of energy. While they escaped to the TARDIS, the Doctor sped over with Hayden, causing Frank's death by making him absorb an excessive amount of energy from the TARDIS. Returning to the Foundation, the present-day Roanna being sent back to the past, the group learned the truth about Hayden's assistant Maria: she was an avatar for Arabella Hendricks, CEO of the Fulcrum Corporation, who was tailoring the Surge to be effective against Dalek weaponry.
Arabella teleported away, leaving the mutated Roanna to rampage through Chicago. She was stopped by the Doctor, Hayden, and Valarie, and was reverted by being fitted with an energy regulator. The group found the older Valarie, injured and near-death, and took her to the TARDIS, but they were unable to prevent her from passing away. (AUDIO: All's Fair)
The Sidewinder Syndicate's ancestors were stranded in Chicago during the 1920s and adopted the method and mannerisms of the Chicago gangsters enthusiastically. (AUDIO: House of Cards)
In 1931, the Master lived in Chicago as gangster Duke Dominus, but his plan was unknowingly defeated by the Fourth Doctor. (PROSE: The Duke of Dominoes)
In 1940, Cody McBride left his home town of Chicago for London. (PROSE: Illegal Alien)
In 1954, Bo Didley recorded the song "Mona" in a studio in Chicago. (PROSE: Cat's Cradle: Warhead)
Trey Korte was born in Chicago in 1970. (PROSE: Business Unusual, Instruments of Darkness)
On 23 February 1973, Major Geoffrey Redvers arrived home in Chicago from his post in Saigon. (PROSE: Nuclear Time)
In 2006, the First Doctor, Susan Foreman, Ian Chesterton, and Barbara Wright arrived in Chicago in the TARDIS. After the Doctor lost the TARDIS in a bet, the time travellers started a 2,500 mile trip to California in order to retrieve it. After doing so, they returned to Chicago by aeroplane. (PROSE: Mother Road)
In 5019, Virginia O'Helsing was living in Chicago at 115 West Ninety-Fifth Street. (PROSE: Possum Kingdom)