The most densely populated place in the United States, as of April 1, 2010, is Friendship Heights Village (a Census Designated Place, or CDP), in Maryland. Friendship Heights is a small, 38 acre neighborhood on the border of the District of Columbia. Population = 4,698; Area = 0.059 square miles; Density = 79,627 persons per square mile (ppsm).
So, Friendship Heights is the densest “place.” And the densest “town or village” is Guttenberg, New Jersey (57,020 ppsm).
And the most densely populated “city” (incorporated place) is Union City, New Jersey. Or as the Census Bureau would call it: “Union City city”.
New York, New York, a helluva town. The Bronx is up but the Battery’s down. New York is the seventh most densely populated place in the USA, and also the most populated place. New York is actually an incorporated city, not a town.
New Jersey leads the list with six of the ten most densely populated places in the USA.
The densest place in California is Maywood, California in Los Angeles County, with a population of 27,395 in a land area of 1.178 square miles (23,256 persons per square mile).
The most densely populated place in the nine-county San Francisco Bay Area is the Rollingwood CDP in Contra Costa County (population=2,969; 0.166 square miles; 17,885 ppsm). Number two in the Bay Area is San Francisco (population=805,235; 46.873 square miles; 17,179 persons per square mile). San Francisco is the 31st most densely populated place in the USA.