The place where the novel takes place is only identified as the "city," with no name ever given. It seems to be a place with good weather, and it also seems to be in what was once the United States. Other than that, we get no specifics.
Bradbury, however, moved to Los Angeles with his family at age fourteen, and lived there into adulthood. He recounts that he had a revelation as he was writing Fahrenheit 451 while he was walking one night on the streets of Beverly Hills. He describes seeing a woman strolling with her husband. The woman had a radio plugged into her ear and was so focused on listening to it that she was oblivious to her surroundings and her spouse. Bradbury, working on Fahrenheit 451 at the time, had thought what he was envisioning might occur in forty or fifty years, but realized it was actually happening as he was writing (from Kingsley Amis, New Maps of Hell: A Survey of Science Fiction).
Given that incident, it may be that Bradbury had L.A. in mind as he wrote, but he is careful not to identify the city in the novel with any that now exists.