WILLIAMSON COUNTY, Texas — A Republican wall in counties along the interstate-35 corridor cracked a little Tuesday night.

Suburban areas like Williamson and Hays Counties overwhelmingly supported Democrats in the midterms election.  

County GOP Chair Bill Fairbrother said he was "surprised and disappointed by the results."

Both the Democratic and Republican chairs agree that the county's shift this election cycle from red to blue is a result of a growing population.

Georgetown Chamber of Commerce CEO Jim Johnson says Williamson County is one of the fastest growing areas in the nation.

"We're ranked in the top six every single time those rankings come out," he said.

Williamson Democratic Party Chair Kim Gilby said a saturated Austin worked to her party's advantage.  

"People move from Austin to the suburbs," Gilby said.  

She attributes the urban sprawl to two flipped State House seats in Williamson County.

Johnson said even though 30 percent of Georgetown residents are senior citizens, millennials are making their way to the area.

"I think there's a large population of young people that like places like the Georgetown Square. They like the feel of it. We're close to 130 so you can commute in, so there's a lot of opportunity for that younger demographic," Johnson said.  

Fairbrother says new residents are seeking a quiet, safe community with a small-town feel.  

"It was Republican leadership that made all of those things possible," he said.

While he feels confident the Democratic gains will be short-lived, Gilby says the blue takeover is only beginning in Central Texas, and beyond.

"It's just a matter of when Texas goes blue," Gilby said.  

In Hays County, Democrats also flipped a Republican State House seat.

Voters also favored U.S. Senate candidate Beto O'Rourke over Ted Cruz by 15 points.