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"): Valhalla is a hamlet and census-designated place (CDP) located within the town of Mount Pleasant, in Westchester County, New York, United States, in the New York City metropolitan area.
Relevant evidence: Yes