 A novel by who is about a time traveler who attempts to prevent the assassination of President John F. Kennedy that has a a fictional town reappeared as late as his  novel?
Derry (Stephen King):  Derry first appeared in King's 1981 short story "The Bird and the Album" and has reappeared as late as his 2011 novel "11/22/63" (see list below). 11/22/63: 11/22/63 is a novel by Stephen King about a time traveler who attempts to prevent the assassination of President John F. Kennedy, which occurred on November 22, 1963 (the novel's titular date).
Stephen King