The Census Bureau identifies two types of urban areas: “urbanized areas” of 50,000 or more people and “urban clusters” of at least 2,500 and less than 50,000 people. There are 486 urbanized areas and 3,087 urban clusters nationwide.
The nation's most densely populated urbanized area is Los Angeles-Long Beach-Anaheim, Calif., with nearly 7,000 people per square mile. The San Francisco-Oakland, Calif., area is the second most densely populated at 6,266 people per square mile, followed by San Jose, Calif. (5,820 people per square mile) and Delano, Calif. (5,483 people per square mile). The New York-Newark, N.J., area is fifth, with an overall density of 5,319 people per square mile. (See sortable lists.)
Of the 10 most densely populated urbanized areas, nine are in the West, with seven of those in California. Urbanized areas in the U.S., taken together, had an overall population density of 2,534 people per square mile.
The New York-Newark area continues to be the nation's most populous urbanized area, with 18,351,295 residents. Los Angeles-Long Beach-Anaheim is the second most populous (12,150,996), followed by the Chicago area (8,608,208). These areas have been the three most populous since the 1950 Census, when urbanized areas were first defined; however, at that time, Chicago was the second largest. Los Angeles became the second most populous urbanized area in 1960, and the order of the top three has not changed since.
Take into consideration the fact that this is an earthquake prone region where much of the land consists of mountains and canyons that are poorly suited for construction and these numbers become even more remarkable.