So what caused the growth? According to the Census Bureau, "domestic migration" or people who moved there, was the biggest driver of growth for Idaho and Nevada, while more births than deaths are the reason Utah landed in the no. 3 spot.
Overall, the US population grew by 2.3 million or 0.72% during the same measurement period, while international migration dropped by 1.8% (the first decrease since 2013). And some states saw no growth at all. In fact, eight states -- North Dakota, West Virginia, Hawaii, Alaska, Illinois, Wyoming, Louisiana, and Mississippi -- actually declined in population. It's also worth nothing that Illinois, which had long been the fifth most populous state in the country, has dropped to number six this year, knocked out by Pennsylvania.