She said the server was handed over voluntarily, under an agreement between Platte River and Clinton's presidential campaign, with no subpoena.
The handing over Clinton's personal server Wednesday was first reported by the Washington Post.
On Tuesday, the Intelligence Community's inspector general notified senior members of Congress that two emails randomly sampled from Clinton's server contained sensitive information that was later given a "Top Secret" classification, while two others contained classified information at the time they were sent. The emails with information subsequently classified as "Top Secret" were forwarded to Clinton, according to the State Department.
Clinton has maintained that she never used her private account for classified information.
The State Department is in the process of reviewing and releasing some 30,000 emails that were sent during Clinton's time at the State Department.
Republicans, who for months have called on Clinton to turn the server over to an independent third party for review, welcomed the news with skepticism.
"It's a welcome development, but it's hard to believe that the Clinton private server and the thumb drives ... have just recently been turned over to the authorities," Sen. Chuck Grassley, R-Iowa, wrote in a statement. "That's a long time for top secret classified information to be held by an unauthorized person outside of an approved, secure government facility."
As the House Select Benghazi Committee continues its investigation into the 2012 compound attack and prepares for Clinton's Oct. 22 testimony, Grassley and other Republican leaders have expanded inquiries into the securing of classified information on Clinton's email server.
Sen. Ron Johnson, R-Wisconsin, the chair of the Senate Homeland Security and Governmental Affairs Committee, has written to the president of Platte River, requesting more information about security procedures and communications between the company and the State Department regarding Clinton’s server. He's also asked for the company to provide the committee with a staff-level briefing on the company's work with Clinton's server.
Clinton confidante Huma Abedin is also coming under scrutiny, after Clinton revealed earlier this week that Abedin also kept a private email address on her home server. Clinton's top aide is cooperating with congressional inquiries and requests from federal judges for official State Department records and emails, according to her attorney, and plans to produce all requested records by the end of August.