The first time Ginnie Cooper walked into the Martin Luther King Jr. Memorial Library for a conference of librarians in the mid-1990s, a rodent scurried across her path in the dank confines of the building’s fourth-floor executive suite.

“I remember thinking at that moment: Oh my gosh, I am so glad I don’t work here,” Cooper said last week, her final week as the chief of the D.C. Public Library.

The District’s central library has been, by all accounts, greatly improved in Cooper’s seven years at the helm — thanks to improvements as modest as replacing light bulbs and signs, and as innovative as installing a bookbinding machine and “3-D printer” for the public’s use.

An even more dramatic makeover is on tap, with a conceptual plan in place to wholly renovate the 40-year-old Ludwig Mies van der Rohe structure and more than $100 million budgeted to carry it out.

Those accomplishments alone might be enough to secure Cooper’s place in the hearts of the city’s library patrons, but they are easily overshadowed by the library system’s other advances: An ambitious capital campaign that has rebuilt or renovated 14 libraries, with three others slated for improvements, and a significant expansion of operating hours that has kept those buildings open longer than ever before in the city.

“What you have done is absolutely transformed our library system in a way that I’m not sure we even could have imagined,” Mayor Vincent C. Gray (D) told Cooper at a farewell reception Wednesday evening at the Harman Center for the Arts.

Cooper has been the face of that transformation, which began in the second term of then-Mayor Anthony A. Williams with the appointment of a blue-ribbon commission in libraries. Leaders of that group, then-Federal City Council director John W. Hill Jr. and developer Richard H. Levy, recruited her from a better-paying job leading the Brooklyn libraries with the promise of building a new central library to replace MLK — which Williams considered “a brooding, run-down mess.”

But Williams’s plan never gained traction with successor Adrian M. Fenty — leading Cooper, for a time, to second-guess her decision to leave New York. But the resources were redeployed into the neighborhood libraries, including the hiring, in several cases, of world-renowned architects to design new buildings.

As the rebuilding campaign proceeded under Cooper’s tenure, library usage grew steadily, even amid shrinking budgets during the economic downturn.

Circulation has grown from 1.2 million items in 2006 to 3.4 million in 2012. When the library in 2008 started tracking attendance for its programs, it estimated about 192,000 yearly participants; that number now stands at nearly 260,000, and the number of community meetings hosted has more than doubled.

The number of public-access computers has grown more than tenfold, and the library now offers a wide array of digital holdings for public use, including e-books and music downloads. The library’s computerized circulation system has been greatly improved, and more emphasis has been placed on children’s programs — particularly for the youngest ones.

“The thing about being a library director is that I do almost nothing,” Cooper said. “I don’t tell stories to kids. I don’t show people how to use a computer. I don’t design beautiful buildings. But I have the opportunity to try to organize the world so that people can do all of those things. And there was a lot that needed to be done.”

Cooper, 68, will move to Portland, Ore., where she previously oversaw the county libraries and where her husband, Rick Bauman, lives. Cooper says she is “going to go seek other delights,” not necessarily in the realm of libraries.

Joi Mecks, the library system’s communications director, has been named interim director while the search for Cooper’s successor is completed. Hill, who is now the library board’s chairman, said last week that the search is in its final stages, and the board could make an announcement as soon as this week.

The highest-profile task for the new chief librarian will be managing the renovation of the central library. The system is seeking architects, and the project has gained the attention of nationally and internationally renowned firms. But the proposed method of financing the project, by adding new floors to the Mies building and leasing them to private parties, has been controversial among some library supporters.

Cooper said there are “lots of hard choices that need to be made” and many supporters must be cultivated to bring the plan to fruition. But she said she is confident the board will find the right person for the job.

“The joke is that they hired me, in part, with the enticement of doing a new central library,” she said. “Isn’t it nice they get to use that enticement for the next person, too?”