Why does New Jersey have the highest population density in the US?

The answer is fairly simple. Lots of people (11th in total population) in a very small state (47th in total area) equals very high population density (1st in the US). By comparison California has the most people (1st in total population) in the 3rd largest state which produces a modest population density (11th in the US) while Alaska which has a vast amount of area (1st in the US) and a very modest number of people (47th in the US) has the lowest population density with about a square mile or 640 acres for each resident and ranks 50th in population density.