It was in this episode that Roy Thinnes met his future wife, Lynn Loring. whom he married one month after this episode aired.
The flying saucer landing site is a fictional West Virginia field called Idlewild Flat. Idlewild was the original name of JFK Airport.
David Vincent ( Roy Thinnes) tells Madeline Flagg (Lynn Loring) he would drive her "all the way to Wheeling", which is a town in the upper panhandle area of West Virginia. It lies along the Ohio River in the foothills of the Appalachian Mountains. In 1967 when this episode aired it had a population of about 50,000. By 2018 the city population had been nearly cut in half and only about 27,000 lived in Wheeling.
Robert Walker Jr previously appeared in the Star Trek story Charlie X as Charlie, a survivor of a decimated human colony who has developed psychic powers which he terrorizes the Enterprise crew with.