Population Density of Big Counties and Counties That Attract the Most Immigrants
April 13,
2018 by Laurie Northington in General 
This is the third factoid in a series of four factoids detailing the migration of the U.S. population to populous cities, creating a Big and Small America. From the 2016 Population Estimates Report done by the U.S. Census Bureau, over 50 percent of residents live in just 143 counties (Big America) with the remaining 50 percent spread out over a vast area encompassing 2,999 additional counties (Small America).
Population Density
The staggering population density in the Northeast is a current key geographic characteristic in the U.S., notably in the New York-Jersey City-White Plains, NY-NJ MSA five key counties. With the exception of San Francisco County, CA, the Northeast contains the most congestion of people with Boston, MA, Philadelphia, PA and Washington-Arlington-Alexandria, DC-VA-MD-WV MSA’s all containing over 11,000 people per square mile.
Meanwhile, the vast areas of California, Nevada and Arizona make the density in their counties less than .05 percent as dense as the Northeast. For example, New York County (New York City) has almost 72,000 people per square mile living in the county, compared to 2,500 in Los Angeles County, the largest county in population in the United States.
Immigration to Big Counties
Slightly less than one million people immigrated to the U.S. last year, down 3.6 percent from 2015. They represented about 45 percent of U.S. population growth. As shown in Table I, big counties were the major recipients with 74.1 percent of immigrants residing in highly populated areas.
Source: U.S. Census Bureau, 2016 Population Estimates, Population Density = the number of persons per square mile in the county