The fictional New England town in H. P. Lovecraft’s The Shadow over Innsmouth is Innsmouth. In the novella, it is a decaying seaport in Massachusetts, isolated by salt marshes and surrounded by rumors about its inhabitants.
The narrator visits Innsmouth during an antiquarian tour and learns that the town was once prosperous through shipping and shipbuilding. Its fortunes decline after the War of 1812, but merchant Obed Marsh later establishes a gold refinery and introduces the Esoteric Order of Dagon. The town’s secret history involves human residents breeding with the fish-like Deep Ones.
Innsmouth is not the same as Lovecraft’s other recurring fictional locations. Arkham and Kingsport are neighboring or related settings in his broader fictional geography, while Dunwich is the setting of a separate story. Lovecraft wrote the novella in 1931, but it was published in book form in 1936. The town was partly inspired by his impressions of Newburyport, Massachusetts.