Birthrates in the United States have reached a historic low, with women having an average of 1.6 children in their lifetime. However, while some states have seen significant reductions in population growth, others are seeing their populations boom.

Since 2020, one of the fastest growing states in the U.S. has been Idaho, increasing by 6.2 percent between 2020 and 2023, according to data from the U.S. Census Bureau. This represents a rise from 1,849,339 in July 2020 to 1,964,726 in July 2023. However, this growth has not been even across the state.

The map below shows which Idaho counties are growing the fastest:

The fastest population growth was seen in Camas County, with a 14 percent increase between 2020 and 2023. This was followed by Boundary County at 12 percent. Tied for third place was Adams County, Boise County, Bonner County, and Canyon County, with an 11 percent growth rate.

So, what might be driving these increases?

According to researchers at the University of Idaho, more than a quarter of the state’s growing population are new to the state. By analyzing vehicle registration and license surrender data from the Idaho Transportation Department between 2011 and 2021, the team found that nearly half a million Idaho residents had moved to the state in the last decade.

“We’re not in the middle of nowhere anymore,” Jaap Vos, a professor in the College of Natural Resources at the University of Idaho who focuses on planning, said in a statement on the university’s website in 2022. “We’re actually in the middle of all the action. If you look at the numbers, you can see we are getting new people coming in constantly.”

According to the Idaho Department of Labor in March 2023, net migration into the state accounted for 88 percent of Idaho’s population growth between 2021 and 2022, the majority of which were U.S. citizens moving in from other states. The remaining 12 percent was from natural change when birth rates overweigh deaths.

While Idaho is seeing this influx of new people, many longstanding Idaho residents have been increasingly moving elsewhere, resulting in a significant reshaping of Idaho’s demographics.

According to a January interview with Matthew Hurt, an economist at the Idaho Division of Financial Management, with the Idaho Statesman, two thirds of Idaho’s predicted revenue growth through the 2028 fiscal year will be added through migration, with as many as one third of migration in Southwest Idaho coming from California.

For every Idaho family that moves to California, Idaho gets three back, Hurt added.

“California totally dominates the net migration story, and it really is because Californians come to Idaho,” he said. “Idahoans don’t really go to California.”

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