Although this was the first aired episode of The Twilight Zone (1959), it is not the first one written. Rod Serling wrote an episode called "The Happy Place", which was rejected because of its subject matter (a society where people were executed when they turned 60), which was considered too depressing.
The scene where Mike Ferris becomes trapped in the telephone booth was based on an incident which happened to Rod Serling. Serling was at an airport, making a call when he heard the boarding announcement for his flight over the intercom. Trying to get out of the booth, he started pushing on the door, forgetting in his panic that phone booth doors open by pulling the door's handle, inwards. Serling waved down a passerby for help, and the man kicked in the door. Though Serling found his mental lapse embarrassing, he incorporated it into this episode.
When Mike leaves the mannequin factory building and looks around, the shoot is of a very familiar town square. The set has been used for decades - it was later used in Bye Bye Birdie (1963) (during the number, Honestly Sincere), Support Your Local Sheriff! (1969), the Back to the Future (1985) films, and TV shows too numerous to count or mention as well as films. The courthouse was also used in the Academy Award winning movie "To Kill a Mockingbird (1962)", and the town set was known as Mockingbird Square before it became associated with the "Back to the Future" series.
According to Rod Serling, while discussing this episode during a 1975 lecture at Sherwood Oaks College, Earl Holliman was running a fever of over 100°F during the filming of this episode.
Rod Serling was not the original narrator for either this pilot episode or the series. Announcer Westbrook Van Voorhis recorded the original narration and was expected to remain on as the series narrator. Due to multiple contractual obligations, Van Voorhis decided he could not commit to the series and withdrew from the show. CBS Producer William Self felt that Van Voorhis sounded too pompous and unconnected to the show's science fiction theme, anyway, and looked for a more suitable replacement to narrate the show. He sought out Orson Welles, however Welles wanted too much money to do it. 'Finally,' said William Self, 'Rod himself made the suggestion that maybe he should do it. It was received with skepticism. None of us knew Rod except as a writer. But he did a terrific job." Serling overdubbed Van Voorhis and became the permanent narrator.