The fictional town in Stranger Things is Hawkins, Indiana. The series begins when Will Byers disappears, drawing his friends, family, and police chief Jim Hopper into a conflict involving a secret laboratory and another dimension.
Hawkins is portrayed as a quiet rural town where unusual events are easy to dismiss because residents believe that nothing important happens there. Hawkins National Laboratory, located nearby, secretly conducts experiments involving paranormal phenomena and human subjects. Those experiments help open a gateway to the Upside Down, a hostile parallel realm central to the series.
The Duffer Brothers originally developed the project under the working title Montauk, with a setting on Long Island. They later moved the fictional setting to Indiana, while filming primarily around Atlanta, Georgia. Jackson, Georgia, served as the basis for Hawkins in many exterior scenes.
Hawkins is not the same as Sunnydale from Buffy the Vampire Slayer, Derry from Stephen King's stories, or Haddonfield from the Halloween franchise. It is specifically an invented Indiana town, with the first season opening on November 6, 1983.