“The Man of the Crowd” is set in London in the 19th century. This period saw a great boom in city populations. With the new technology of the Industrial Revolution came new factory jobs, and many people moved from small towns and villages in the countryside to urban centers like London in search of work. This kind of mass migration to urban centers meant that people who were very different from one another suddenly found themselves sharing spaces in a way they hadn’t before. "The Man of the Crowd" reflects this social change, and the narrator spends a lot of time describing the diverse crowds of the city, where people from all social classes and backgrounds mingle in a shared urban space.
London was the largest city in the world in 1840, when Poe wrote “The Man of the Crowd,” so it follows that he would have used it as the setting rather than an American city—at the time, it was seen as the epitome of all things industrial and urban. Poe also spent part of his childhood living in London, and it’s possible that his descriptions of London in this story were drawn from his memories there.
