Loudoun County library officials anticipate that the long-awaited Gum Spring Library, which will have its grand opening Saturday, will quickly become the busiest of the county system’s eight branches.

Gum Spring is the first library branch in the rapidly growing Dulles South area. It is also the first branch in Loudoun to be built through a public-private partnership, with Stone Ridge developer Van Metre Homes, without using funding from taxpayers.

Supervisor Matthew F. Letourneau (R-Dulles) said the importance of the library, at 24600 Millstream Dr. in Stone Ridge, to the Dulles South area cannot be overstated.

“A lot of folks in the Route 50 corridor use the Fairfax system, not that that’s especially close, but it’s closer,” Letourneau said. “So for communities ranging from Brambleton and Loudoun Valley Estates, all the way down to South Riding, Stone Ridge, Kirkpatrick Farms . . . this is going to be their library.”

Karen Montgomery, chairman of the Friends of the Gum Spring Library, said she expects the opening to be “one of the most exciting days I’ve ever experienced.”

“I’ve been working on this board since its inception [in 2006], and I’ve been advocating for this library since ’97, so this is something that has been near and dear to my heart for a very long time,” she said.

Letourneau credits former Dulles District supervisor Stephen J. Snow with being an early advocate of the public-private partnership. Snow, who died in 2011, favored using proffers from developers to finance the construction of roads and other public projects.

Snow was a member of the Board of Supervisors in 2006, when Van Metre applied for a rezoning in Stone Ridge. At the time, plans called for the county to build a smaller library on a proffered seven-acre site in Stone Ridge. Montgomery, Snow’s appointee to the Library board of trustees, said the county decided that a larger regional library would better serve the needs of Dulles South.

During the rezoning negotiations, Van Metre agreed to construct the building shell and give the county the bottom two floors of the building for the library. Van Metre also proffered the design of the library; the county was responsible for outfitting the interior.

In a November 2007 referendum, county voters approved a $7.1 million bond issue to finance the county’s construction costs for the library. It was anticipated that the library would open in 2008. But construction was delayed until development-based triggers written into the proffer agreement were met, Montgomery said.

“We knew [the public-private partnership] would give us a bigger library, and it would get it to us cheaper, and we thought it would get it to us faster,” Montgomery said. “The first two of those are true, but the third one did not turn out to be true.”

Paul Brown, assistant director of the county’s Department of Transportation and Capital Infrastructure, said the bonds approved in 2007 were never issued because the county was able to fund its share of the project using about $9 million in cash proffers from developers in the Dulles area.

“You’re talking basically, a $20 million project,” he said, including the value of the 40,000 square feet of library space proffered by Van Metre. “This whole library was built 100 percent through in-kind and cash proffers from the development community, at no expense to the taxpayer.”

The library has a 3,000-square-foot teen center, community meeting rooms, Wi-Fi access and 60 public computer stations.

“The children’s section is almost the size of the Ashburn Library,” Letourneau said. “The entire first floor is children’s, and if you know the demographics in the Dulles South area, that’s really where the need is.” He predicted that the teen center will also be heavily used.

“We’ve had an issue over the years with there being not a lot of places for young people to go in that area,” Letourneau said. “So this is going to be sort of a community focal point.”

Chang Liu, director of the county public library system, said that library staff members have been doing outreach at public events in the Dulles South area to prepare residents for the opening of Gum Spring. Staff members discovered at the events that “almost every single person that came to the booth did not have a library card,” she said.

“The teen and children’s staff have also been going out to the schools in the area,” Liu said. “They have literally visited every single school and given out library cards.” She said the library has also reached out to the home-school population. Staff members have issued about 900 cards at the school and community events.

The grand opening will be at 11 a.m. Saturday. Scheduled speakers will include members of the Board of Supervisors, the library board of trustees and the Friends of the Gum Spring Library.