New York’s population dropped slightly between July 2015 and July 2016 — the first dip in a decade — according to new population estimates released Tuesday by the U.S. Census Bureau.

And while the nation’s population grew by 0.7 percent in that time, the growth was at the slowest rate since the Depression era.

Demographers are looking at the aging of the population and opportunities in other parts of the nation as among the reasons for the recent stagnation in the state’s population.

New York’s population was estimated at 19,745,289 on July 1, 2016 — down from 19,747,183 a year earlier, for a loss of nearly 1,900 people.

New York still remained the fourth most populous state in the nation, behind California, Texas and Florida. Florida supplanted New York as the third most populous state in 2014.

An estimated 191,367 people left New York for other states between July 2015 and July 2016 — a loss that was not overcome by an influx of 118,478 people immigrating to New York from other countries.

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New York was one of eight states that lost population during that one-year period, the bureau said — a loss that followed population gains for the state during the previous five years.

Policymakers should be concerned about those numbers, said Christopher Jones, senior vice president for the Regional Plan Association, a Manhattan-based research and advocacy group focused on the tristate metropolitan region.

“We don’t really know what’s causing it,” Jones said of New York’s population decline. “It could be from increasing housing prices. It could be that job creation is happening quicker in other parts of the country than here. A likely possibility is more people are reaching retirement age and moving elsewhere — Florida and other states.”

Jones said he’d need to wait for the bureau to release county-level population estimates next year to get a better sense of the reasons behind the changes.

“The pattern for the last several years is you’re seeing population growth in the downstate areas — New York City, Long Island and Westchester — and population declines in upstate New York,” he said. “It’s likely that that’s continuing. But we don’t know if this is because population growth is slowing downstate or population decline is accelerating upstate.”

Jan Vink, a researcher at Cornell University’s Program on Applied Demographics, said during the 2007-09 recession, the state’s “domestic migration slowed down, which was good for New York.”

Now, with a rebounding economy, he said migration is “picking back up.”

Vink added that domestic migration losses were even bigger than they are now. The university’s program is affiliated with the Federal-State Cooperative for Population Estimates, which works with the Census Bureau.

Similarly, William Frey, a demographer and senior fellow at the Brookings Institution in Washington, D.C., said in an email that “high cost” states like California and New York “held on to potential outmigrants” during the recession and “are now growing more slowly as more migrants are heading to growing parts of the Sun Belt.”

Frey and Vink also noted the impact of changes in births and deaths.

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“It’s more the deaths are increasing” than births are decreasing in New York, Vink said. “It has to do with an older population.”

Meanwhile, the nation’s population was estimated at 323.1 million on July 1, 2016, the Census Bureau said.

“States in the South and West continued to lead in population growth,” said Ben Bolender, chief of the bureau’s Population Estimates Branch.

Frey said the nation’s rise in population between 2015 and 2016 was the slowest rate since 1936-37, a statistic that was confirmed by the Census Bureau.

The nation’s population “slowdown since last year has to do with a decline in the rate of natural increase . . . which is a result of a downturn in births and rise in deaths. . .” Frey said. “It’s the aging of the population that is leading to lower national growth rates.”