A couple of facts about population density that I came across while my girlfriend was behind the wheel on some long drives up and down the east coast. First if Texas (268,820 square miles) were as densely populated as New Jersey (1,134 per square mile) it would contain about 305 million people—essentially the entire population of the United States. Second, if the entire state of Maine (35,385 square miles) were as densely populated as the city of Somerville, Massachusetts (18,147 per square mile) it could hold over 640 million people.
To reach for a policy point here, the Texas/Jersey thing illustrates that it would be possible for the United States to contain a lot more wilderness without jamming everyone into super-dense cities. New Jersey is the quintessential suburban state. The Maine/Somerville thing mostly illustrates the point that Somerville is a lot denser than you might think from a casual walk around the place. Somerville’s denser than Chicago or San Francisco or Philadelphia or DC without having much of anything in the way of really tall buildings. It turns out that modest-sized structures can create tons of density as long as the structures occupy a lot of the territory.