Despite having a population of about 318 million people, 47 percent of the USA remains unoccupied.
A Block is the smallest area unit used by the U.S. Census Bureau for tabulating statistics. As of the 2010 census, the United States consists of 11,078,300 Census Blocks. Of them, 4,871,270 blocks totaling 4.61 million square kilometers were reported to have no population living inside them.
This map, with areas shaded in green, shows where there is zero population in the United States:
Very curious is how you can distinctly see the border boundary of North Dakota (it is more apparent than the boundary of any other state). Why? Mapsbynik provides a clue:
On a more detailed examination of those two states [North Dakota, South Dakota], I’m convinced the contrast here is due to differences in the sizes of the blocks. North Dakota’s blocks are more consistently small (StDev of 3.3) while South Dakota’s are more varied (StDev of 9.28). West of the Missouri River, South Dakota’s blocks are substantially larger than those in ND, so a single inhabitant can appear to take up more space. Between the states, this provides a good lesson in how changing the size and shape of a geographic unit can alter perceptions of the landscape.
Books I Read 
It’s a good thing that a lot of that is green. Wilderness is very important. Here in Japan, I think a large percentage of Japan’s land is uninhabited, as it’s mostly mountains. A quarter of the people, or about 36 million, are living in the greater Tokyo area, including me.