New York County has the same boundaries as the Borough of Manhattan (Manhattan Island). As such, it is the most densely‑populated county in the United States.
Photo: Houses at 208-218 East 78th Street, New York, N, south of the village of Millerton. Listed on the National Register of Historic Places in 1983. Photo by wikipedia username: Daniel Case, 2008, own work, creative commons [cc-3.0], via wikimedia commons, accessed November, 2022.