Derry, Maine is a fictional town and a part of Stephen King's fictional Maine topography, and, like Castle Rock, it has served as the setting for a number of his novels, novellas, and short stories.
It first appeared in the short story "The Bird and the Album" and was expanded on in both It, Insomnia, and 11/22/63. Derry is said to be near Bangor, Maine, but King has acknowledged that Derry is actually his portrayal of Bangor. A map on King's official website, though, places Derry in the vicinity of the town of Etna.
Both Derry and Castle Rock, when joined with Jerusalem's Lot, complete a trinity of fictional towns King has created as central setting points; the three exist as the main setting in more than one work. King has created other fictional Maine towns such as Chamberlain in Carrie, Ludlow in Pet Sematary and The Dark Half, Haven in The Tommyknockers, Little Tall Island in Dolores Claiborne and Storm of the Century, and Chester's Mill in Under the Dome. However, these fictional towns have not been used as much as Derry, Castle Rock, and Jerusalem's Lot in King's stories. This trinity of locations is an homage to H. P. Lovecraft's use of Arkham, Dunwich, and Innsmouth, three fictional towns or cities in Massachusetts.