The latest population projection forecast shows the six-county Central Texas region covered by the Capital Area Metropolitan Planning Organization could swell to more than 4.1 million people by 2040.

On June 10, the CAMPO policy board approved using population forecast data from the Texas State Data Center in its planning efforts for its 2040 long-range transportation plan. CAMPO staff reviewed five possible population forecast scenarios, including one each from the state comptroller and Texas Water Development Board, but ultimately recommended the board approve the most aggressive forecast prepared by the TSDC.

This decision stems from CAMPO staff finding that population projection forecasts used in the 2020, 2025, 2030 and 2035 long-range plans came in under actual census population estimates.

The new scenario indicates Travis County's population could grow from 1,024,000 in 2010 to 1,733,000 by 2040. Williamson County could increase in size from 423,000 in 2010 to 1,407,000 by 2040. Hays County could quadruple in size from 157,000 in 2010 to 628,000 by 2040. The six-county region, which also includes Bastrop, Burnet and Caldwell counties, had 1,759,000 people in the 2010 census.

Hays County Commissioner Will Conley, chairman of the CAMPO policy board, said the new scenario drastically changes population projections for the region.

"We have blown every population projection out of the water in [Hays] County," he said. "I think these will get us closer to the reality of what's going on."

Austin was recently named the 11th-largest U.S. city after previously being ranked 13th in size, according to the U.S. Census Bureau.

Population and employment data are used for travel forecasting to predict where future traffic issues will occur, said Daniel Yang, CAMPO's geographic information systems and modeling program manager.

Yang said that when population projections are made, the previous decade's actual population numbers are used to determine trends. He said population forecasts approved in 1993 and 1998 have been lower than census population numbers. CAMPO updates its long-range plan every five years and approves updated population and employment data to use in the new plan.

Click here to download the full population forecast report.