The book is famous for its rich depiction of New Orleans and the city's dialects, including Yat. Many locals and writers think that it is the best and most accurate depiction of the city in a work of fiction.
The city described in the novel differs in some ways from the actual New Orleans. The first chapter mentions the sun setting over the Mississippi River at the foot of Canal Street. As this direction is to the south-east, this is impossible in reality. Possibly this is a joke by Toole related to the fact that the area across the river is known as the "West Bank", despite the fact that because of the twists of the river it is actually to the south or east from parts of central New Orleans. Such details are not likely to be noticed by people who are not familiar with New Orleans.
A bronze statue of Ignatius J. Reilly can be found under the clock on the down-river side of the 800 block of Canal Street, New Orleans, the former site of the D. H. Holmes Department Store, now the Hyatt French Quarter Hotel. The statue mimics the opening scene: Ignatius waits for his mother under the D.H. Holmes clock, clutching a Werlein's shopping bag, dressed in a hunting cap, flannel shirt, baggy pants and scarf, 'studying the crowd of people for signs of bad taste.' The statue is modeled on New Orleans actor John "Spud" McConnell, who portrayed Ignatius in a stage version of the novel.
Various local businesses are mentioned in addition to D. H. Holmes, including Werlein's Music Store and local cinemas such as the Prytania Theater. Some readers from elsewhere assume Ignatius's favorite soft drink, Dr. Nut, to be fictitious, but it was an actual local soft drink brand of the era. The "Paradise Hot Dogs" vending carts are an easily recognized satire of those actually branded "Lucky Dogs".