New state estimates show Utah’s population continues to boom — adding 59,045 people this year, the equivalent of plopping in another Taylorsville. But demographers see a radical shift in what fuels that growth.

Mainly, traditionally big-family Utah is seeing fewer births: they dropped by 1,202 last year, continuing a nine-year streak of declines. Meanwhile, migration accounts for more of the state’s growth as its healthy economy serves as a magnet to job seekers.

“Natural increase,” or births minus deaths, created 54 percent of Utah’s population growth over the past year — down from historical averages of around 66 percent. (And in 2010 amid the Great Recession, it accounted for 95 percent of Utah’s total growth).

“Natural increase is still strong. It’s still the major share of growth. But it’s been going down steadily since the onset of the Great Recession,” said Pam Perlich, director of demographics at the Kem C. Gardner Policy Institute at the University of Utah.

Perlich sees many potential causes for declining births here, even though Utah still has the nation’s top overall fertility rate, according to the U.S. Census Bureau. For one, “We’ve seen a collapse in the fertility rates of teenage women. That’s terrific.”

FILE - In this Wednesday, Nov. 12, 2008 file photo, a baby cries in its bed in a hospital in Bremen, northern Germany. According to as study released on Monday, Oct. 23, 2017 by the Proceedings of the National Academy of Sciences, the way a mother responds to her crying baby seems to be programmed into her brain circuits. Researchers found that mothers across many cultures tend to react the same way to an infant’s cry, and brain scans showed that this distressing sound activates circuitry associated with such responses. (AP Photo/Joerg Sarbach)

She said rates have also come down significantly for women in their 20s. “You see people delaying having children until their 30s, or late 20s. And when you start later, generally you have fewer.”

Perlich said demographers thought that would change as the economy improved after the recession and families could more easily afford more children — but it has yet to do so.

“So it’s not just the economy here. There are other factors at play,” she said. “It could be that women are asked to do more: get more higher education, go on missions. All that is good, but it takes time. So it could lead to these delays.”

Meanwhile, net migration is accelerating — up by 2,728 people from the previous year, for an estimated total of 26,989. Perlich said most come from nearby states, but some comes from around the country and abroad.

“It’s the highest we’ve been since 2006,” Perlich said. “As the economy is growing, it is bringing people to the state for economic and educational opportunities.”

She said the immigrants are also changing Utah.

Steve Griffin | The Salt Lake Tribune 140 people from over 40 countries become new citizens of the United States of America as they take the Oath of Allegiance during a citizenship ceremony hosted by the U.S. Citizenship and Immigration Services at This Is The Place Heritage Park in Salt Lake City on Thursday.

“They are going to bring the characteristics from the outside world, rather than have the characteristics of the population that is already here. That intensifies the change process, the diversification along the lines of culture, nativity, language, ethnicity, origin,” she said.

Some immigrants may also tend to have smaller families than Utah’s traditionally large ones.

The estimates were released Wednesday by the Utah Population Committee — which Perlich heads — and the Gardner Policy Institute. It is funded by the state to generate such estimates with a variety of local data, and act as a watchdog on estimates from the U.S. Census Bureau that affect federal funding in many areas.

The Census Bureau is scheduled to release its own estimates of state populations for 2017 on Dec. 20.

The new state estimates said Utah had a population of 3.1 million on July 1 — up by more than 350,000 since the 2010 Census, or 12.7 percent.

The estimates say Salt Lake County had the biggest numerical population increase among counties over the past year, up by 19,372 people (or 1.7 percent). Wasatch County had the biggest increase by percentage, up 4.1 percent in the year (or 1,227 people).

Perlich said some of the growth in Salt Lake County was different than other recent years — coming not in the suburbs as much as in Salt Lake City itself with “urban in fill” from large new apartments or other multi-family units.

(Rick Egan | The Salt Lake Tribune) The Alta Gateway Station, 100 S. 500 West, Salt Lake City, Friday, September 8, 2017.

Salt Lake and Utah County combined have 56 percent of the state’s total population — but Utah County’s growth is especially accelerating, Perlich said, up by 14,350 people or 2.4 percent in the year.

“Utah County is just leading the charge. It’s definitely where that growth epicenter is” for the state, Perlich said.

Other Wasatch Front counties, plus Washington County, also help account for the biggest growth in the state, she said. Davis County attracted an additional 6,112 people, up 1.8 percent; Weber was up by 3,152, or 1.3 percent; and Washington County increased by 5,230, or 3.3 percent.

Perlich said Washington County’s growth is fueled in part by baby boomers retiring and moving to St. George.

Also, “commuter ring” counties near the Wasatch Front are also seeing big growth. “Wasatch and Tooele County especially are growing rapidly,” she said — likely drawing commuters who want more land, less expensive housing and a better quality of life.

Meanwhile, much of rural Utah has stagnant or small growth. “The energy and natural resource counties especially are struggling,” she said. “Carbon, Emery, Duchesne, Uintah, Garfield, Kane, Piute and San Juan all have very slow growth.”

In several rural counties — Carbon, Daggett, Piute, Rich and Wayne — births and deaths are essentially equal. “That tells you their young people are moving off,” Perlich said.