More than 2 million people will move into Virginia over the next 30 years, but Arlington County, one of the state's wealthiest and fastest-growing localities, will end up with nearly 20,000 fewer residents than it has now.

Arlington's population of 216,000 will drop 10 percent to 197,000 by 2040, according to a new study by the University of Virginia's Weldon Cooper Center for Public Service. Researchers said the expected decline is similar to other population drops Arlington experienced over the past 60 years.

Arlington officials, however, rejected the study's findings.

Past declines in population were caused by a lack of development and mass transit in the 1970s ?-- problems unlikely to be repeated during the next 30 years.

The study also fails to take into consideration how a number of development plans over the next 30 years would affect population, said Elizabeth Rodgers of the county's Department of Community Planning, Housing and Development. Already, a 534-unit housing project, dubbed Virginia Square Towers, has been approved by the County Board, along with a 374-unit project called Central Place, a 188-unit complex called Wakefield Manor and numerous other developments.

The county's own population projections, which do include those various planned developments, show the number of residents rising to 252,000 -- a 14 percent increase.

"Arlington County is so unique and has different development patterns [than other localities in the state]," Rodgers said. "Their formula doesn't fit for us."

Researcher Rebecca Tippett, who worked on the study, defended its results. The center would not have been able to complete the study had it looked at all development projects expected to be completed around the state over the next three decades, Tippett said. Moreover, past studies done by the center using the same methodology have proved accurate, she said.

"The best model is the best model," Tippett said. "But we don't have concrete data for the future. The further out you get, the more uncertainty you have."

The same study shows that other communities around Northern Virginia, the state's fastest-growing region, will see population increases over the next 30 years. Fairfax County, the state's largest municipality, will see its population rise from 1.1 million to 1.35 million, the study shows. Alexandria's population will jump from 144,000 to 149,000.

Fairfax County Director of Public Affairs Merni Fitzgerald said the projected increase was "not surprising."

"We're actively seeking 100,000 more people in Tysons," she said, "and we've got projects slated in all areas of the county: Mosaic, the revitalization of Route 1, and [Metro's] incoming Silver Line."

Virginia's overall population is projected to climb from 8.1 million to 10.5 million by 2040.