The most densely populated block group is one in New York County, New York — 3,240 people in 0.0097 square miles, for about 330,000 per square mile. The least dense is in the North Slope Borough of Alaska — 3 people in 3,246 square miles, or one per 1,082 square miles. The Manhattan block group I mention here is 360 million times more dense than the Alaska one.
As you see, America’s population density vary over a huge range. This is the reason why the electoral maps painted red and blue paint such a skewed picture of the country’s political preferences.