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 Portland was from page 110. This city was located in Maine.
Although the writers presumably intended this to be Portland, Oregon, the script never gave the location of Portland. The Star Trek Encyclopedia (4th ed., vol. 2, p. 290) specifically says that Judith Sisko lived in Portland, Oregon.