New York County is the United States' second-smallest county by land area (larger only than Kalawao County, Hawaii), and is also the most densely populated U.S. county. It is also one of the most densely populated areas in the world, with a census-estimated 2019 population of 1,628,706 living in a land area of , or 72,918 residents per square mile (28,154/km2), higher than the density of any individual U.S. city. On business days, the influx of commuters increases this number to over 3.9 million, or more than 170,000 people per square mile (65,600/km2). Manhattan has the third-largest population of New York City's five boroughs, after Brooklyn and Queens, and is the smallest borough in terms of land area. If each borough were ranked as a city, Manhattan would rank as the sixth-most populous in the U.S.