FAIRBANKS — The Fairbanks North Star Borough has cracked the 100,000 population milestone, but it’s not because of an influx of newcomers.

The Fairbanks area gained about 2,800 new residents between 2010 and 2012, an increase of 2.8 percent, according to figures updated by the Alaska Department of Labor on Friday. That puts the estimated borough population at 100,343.

That growth is attributable to births. The state estimates the area had a small loss in terms of net migration, with 46 more people leaving the Fairbanks area than moving in during the past two years.

State demographer Eddie Hunsinger said it’s a common situation in Fairbanks, which has long had a highly transient population fueled by its heavy military presence.

“In general, Fairbanks has usually had close to zero net migration, but with these big flows in and out,” Hunsinger said.

The high local birth rate is attributable to the types of residents who are entering and leaving the area. Residents in their 50s and 60s make up the bulk of departing residents, while those in their 20s and 30s — the typical childbearing years — make up most of the people moving into the area.

“It’s skewed toward older people leaving and younger people taking their place,” Hunsinger said.

Alaska’s population as a whole grew 3.1 percent from 2010-12, with an estimated 732,298 people living in the state. That’s nearly twice the growth rate of the U.S. as a whole, which grew up 1.7 percent during the same period.

The highest growth area in Alaska, in terms of total population, was the Anchorage/Mat-Su region. The area added about 17,000 residents during the past two years, an increase of about 3.1 percent. That included in-migration of about 7,700 new residents.

The Juneau area had a growth rate of 5 percent, adding more than 1,500 new residents. About 1,000 of that population boost was because of in-migration, according to state statistics.

Almost every region of the state gained population during the past two years. Only Skagway, Yakutat and the Bristol Bay Borough were listed with fewer people, and none of them had a population dip of more than 40 people.

Contact staff writer Jeff Richardson at 459-7518.