A new bit of data from the Census Bureau: Between 2014 and 2015, Houston added 160,000 people to its population -- the largest gain of any metropolitan area in the country and the equivalent of dumping the entire population of Guam into the city's boundaries. Texas had four of the 20 fastest-growing cities, adding 600,000 people in total. Or to put it another way: One Wyoming.

The 100 fastest-growing counties, though, were more interesting -- clustered heavily near the southeastern coast and in oil country.

Most of the population growth is in the Southeast. But much of the largest relative growth is in the Plains.

The county with the biggest percentage of growth was McKenzie County, N.D. North Dakota has consistently been the fastest-growing state in the nation for several years, thanks to the oil boom that fracking unleashed. This is also why counties in Texas have grown, including a number of counties on the outskirts of Houston.

Looking at how these same 100 counties have changed since 2000, you can see how dramatically they've grown. The largest circle here is Pinal County, Ariz., which more than doubled since 2000. (McKenzie is second.)

Of these 100 fastest-growing counties, 85 voted for Mitt Romney in 2012.

There's a reason for this: They grew much more rapidly because they were smaller. They were smaller because they were more rural. And there's a correlation between voting patterns and how rural an area is.

But this also mirrors the broader long-term trend in the United States: South and to the West. Coloring each state by its population rank since 1900, you can see how the Northeast and Midwest have given way to the South and West.

When the West gains more population, does it change the politics of the state or of the people who moved? Which influences which? The answer so far seems to be that it depends on the race and the place. Texas has gotten more Republican, even relative to its very-Democratic past. California has gone the other way.

The story of the fastest growing counties (and cities) is this: People want to move to jobs and good weather. The jobs recently have been in red, rural places. The good weather has been in the South and West, both of which often lean Republican. As always, the political picture is more complex than it may seem.