Chicago

From TARDIS Index File, the free Doctor Who reference.

Chicago is a city in the state of Illinois in the United States on Earth. It is noted for having been home to many gangsters in the 1920s. The Doctor and Ace once went to Chicago and met Dekker. (NA: Blood Harvest)

In 1931, the Master lived in Chicago as gangster Duke Dominus, but his plan was unknowingly defeated by the Doctor. (VD: The Duke of Dominoes)