The location of fictional city in unknown, as it was never mentioned in the film.
It is a walled town where all living things (except the people) are artificial and the air and water are quite polluted.
All the characters except for The Once-ler and The Lorax live there. It was originally named by The Once-ler based on his hit creation, the Thneed. The mayor of the city was Aloysius O'Hare, owner of the O'Hare Air Company.
Role in the Crossover
The fictional city will most likely be used the fandom's modern crossovers that involve Ted, Audrey and the world of The Lorax.