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Utah was the third-fastest growing state in the nation last year, even though its rate of births continues to fall.

SALT LAKE CITY — Utah was among the fastest-growing states in the nation last year, even though its families aren't having as many children as they used to.

The Beehive State came in third, behind neighboring Idaho, which had the most rapid expansion of any state. Nevada ranked second, according to new estimates from the U.S. Census Bureau.

"Utah continues to see a sustainable but strong rate of growth," said Pam Perlich, director of demographic research at the University of Utah's Kem C. Gardner Policy Institute. "It's among the most rapidly growing in the nation, but it's not in a boom situation."

Utah's typically large families are mostly responsible for its 1.9 percent population growth — an increase of about 57,000 people — the Census Bureau announced Wednesday.

Even so, the state's fertility rate — the number of births per each woman of child-bearing age — has declined. For the first time in recent memory, Utah has slipped from its No. 1 spot, according to a different set of newly released data from the Centers for Disease Control.

"That's a big deal," said Perlich. Utah's fertility rate hovered just above 2.23 in 2016, she noted, compared to South Dakota's slight advantage of 2.26.

"It's really surprising" because Utah's economy is healthy, Perlich said. More young people are moving here, Perlich's team has found, but they appear to be delaying childbirth and having fewer kids. More detailed data is expected to provide more insight next month.

Idaho's growth is fueled mostly by newcomers from other states, the Census Bureau said. Its population swelled to 1.7 million — an increase of 2.2 percent, or roughly 36,000 people — over a year-long period ending July 1 2017.

Whatever the reason, the upticks in the Intermountain West come as no surprise to experts.

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"That's continuing a trend that goes back at least until the 1990s, where this area of the country is the most-rapidly growing," Perlich said. Southern states also are experiencing similar growth, while several in the East have held steady.

But one Utah neighbor state has bucked the trend: Wyoming had the largest percentage drop nationwide, of 1 percent.

Despite Utah's growth, it remains very small compared to California, with 39 million residents, and Texas, with 28 million. Both of those states saw population increases in the hundreds of thousands last year.

The takeaway for Utah, Perlich said, is that "growth and change are normal for Utah in the foreseeable future."