Riverdale Asylum is an asylum in New York City, on Earth, in the 20th century.
Benny Russell was detained at Riverdale Asylum following his breakdown in the year 1953. Eli Underwood was also a patient there. (DS9 episode: "Shadows and Symbols", DS9 novel: Unity)
After Russell and Underwood escaped from Riverdale in 1955, the asylum turned them over to the New York Police Department. (ST - Typhon Pact novel: Raise the Dawn)