Fastest growing is relative to what’s already there.
Absolute numbers might tell a more accurate story.
For example, how many new residents are moving to Utah compared to Florida or Texas or N. Carolina? It’s easy for a low number to get a higher percentage than an already established huge number. 10% of 100,000 is 10,000, while 1% of a million is also 10,000.
Colorado has already been swarmed and ruined so they’re going to move on to Utah.
I’ve heard that Utah has a high birth rate, because Mormons tend to have large families. How much population growth is natural increase vs. people relocating to Utah.