PHOENIX — Cochise County lost a larger percentage of its population last year than any other county in the country, new figures from the U.S. Census Bureau show.

The new report, being released today, also found that Maricopa County had the second-highest actual growth rate last year of any county in the United States, adding 68,800 residents. Only Harris County, Texas, where Houston is located, did better, with its population up by almost 83,000.

Pima County, meanwhile, saw a small percentage increase in its population last year compared with the previous year.

The report also showed that if it weren’t for new people moving to Arizona in 2013, some counties would be losing population.

The Census Bureau said there were more people who died last year in four Arizona counties than were born there. Mohave County had a net “natural loss” of 731 residents last year, with Yavapai County not far behind with deaths exceeding births by 726.

Gila County had 148 more residents die than were born there. And tiny La Paz County nearly broke even with a net loss of 52.

Meanwhile, Cochise County’s 1.7 percent population decline — and net loss of 2,262 residents — was not due to natural losses, with births still exceeding deaths there by 465.

Instead, the county shed more than 2,700 residents who the Census Bureau reports decided to move elsewhere, whether another county, another state — or out of the country.

The “why” behind that appears to be related to Fort Huachuca.

“We were fighting two wars,” said Robert Carreira, director of the Center for Economic Research at Cochise College. Most significant, he said, that involved a lot of people working for private defense contractors, many of them former military personnel who found ways to make a lot more on the outside.

“As we’ve wound down these wars, we don’t have as much of a need for these defense contractors,” Carreira said. “So those jobs go away.”

But that’s not all.

“As fewer active military are deployed, you don’t need the civil servants anymore,” he said.

That migration, both domestic and international, played a key role beyond Cochise County in who is living in Arizona, and where.

Perhaps most crucial is keeping the state’s graying counties from simply becoming a collection of ghost towns as their aging populations die off.

In Arizona, about 14.8 percent of all residents are 65 and older. By contrast, nearly a quarter of Mohave County residents fell into that category, with the figure slightly higher than that in Yavapai County.

Looking at it another way, those counties are far more gray.

Consider: The median age of a typical Arizonan is less than 37. Yet for Mohave County, the median age is 49. And it’s even higher in Yavapai County, at 51.

The state’s two largest counties are far younger, with a median age of just slightly more than 35 in Maricopa County and 38 in Pima County.

What kept these aging counties from shrinking — or shrinking more than they otherwise would as residents died off — was inflow from elsewhere.

Mohave County, for example, added 336 new residents from elsewhere. That helped keep the county’s net population loss to just 112.

And Yavapai County managed to grow by more than 2,600 as 3,200 people from elsewhere in Arizona or the rest of the country — and even 117 from other countries — chose to make it their home.

Santa Cruz County found itself in just the opposite situation.

The Census Bureau reported that 864 people moved out, including 47 who left the country entirely. But the county’s birthrate managed to at least partly mitigate that, keeping the total loss to 456 residents.

Overall, the Census Bureau figured that more than 26,000 people moved to Arizona last year from other states, with another close to 10,900 coming here from other countries.

That brought total growth in the state last year to 75,475, bringing the state’s population estimate to 6,626,624, a 1.2 percent year-over-year growth rate.