In the mid-20th century, people, even those in rural areas, could hear about what was happening in this city on the radio. Though people might feel they were far from events, radio brought them in closer. (TNG: "The Big Goodbye")
The pages seen in the episode were actually from the detective novel, The Listening Man, by author John A. Moroso. This novel was published in 1924. Information on Chicago was from page 110.
In "The Neutral Zone", the use of this city as a birthplace came from the remastered Clare Raymond family tree.
This city was named on a German map of the United States (Die Vereinigten Staaten von Amerika) in "Storm Front". Its location was represented by an orange circle. In most states the orange circles marked the state capitals, while in Illinois both Chicago and the actual capital Springfield were marked such.