Short story; punchline is "Chicago"

[Jelly Ree]

This story is from a book 30 or 40 years old.
Set not too far in the future the plot dealt with a nuclear accident that was so devastating, everyone was made to forget it.
A major city had been destroyed.
Someone finally put the pieces together but when they presented their evidence the response was, "Do you expect us to believe there was ever a major city named...CHICAGO"?

Any ideas on title or author?

Thanks

 

[Seli]

The story is (probably): 'What’s the Name of That Town?' by R.A. Lafferty