When it comes to census trends, only the broadest of generalizations are true. The widely disparate populations and topography of America mean that almost anything you can say about one place will be proven untrue in another place. There are multiple counties in the western United States that are larger in territory than entire states on the East Coast. Conversely, there are miniscule counties in New England and the Midwest that dwarf whole regions out in Montana or Alaska.
One thing that can be said for certain is that the center of American population is moving south and west. This has been the truth for decades now. Improving technology makes desert living more comfortable than trying to brave out a harsh winter. It was once the truth that the wide open spaces of the American frontier offered economic opportunity for people as well. However, the other major trend in American demographics strongly suggests that this is no longer the case. No matter where they are located, the persistent flow of population pressure is away from the rural areas and towards the urban centers. It simply does not take as many people to produce food with modern technology. The current trend is for farmers and agricultural laborers to live in town and cities and commute to work, exactly like any other suburban professional.
Practically no other trend remains constant from decade to decade. With the exception of Texas, very few of the fastest growing states or counties in 2000 are among those who are expanding the quickest in 2010. Los Angeles still has the most inhabitants of any county, with 9.9 million people, but it is important to note that Los Angeles County covers nearly 5,000 square miles, an area larger than all of New York City, northern New Jersey, and most of Connecticut combined.