Question: Valhalla is a hamlet and census-designated place (CDP) located within the town of Mount Pleasant, in Westchester County, is a county in the U.S. state of New York, it is the second-most populous county on the mainland of New York, after which location?
Sentence (from "Valhalla, New York"): The name comes from "Valhalla", a heavenly abode in Norse mythology.
Relevant evidence: No