Clinton, who leads Trump in opinion polls, has said she did not compromise classified information and used a private server for convenience. She later apologized, saying: "I take responsibility."
The order by U.S. District Court Judge James Boasberg, who is overseeing a group of lawsuits seeking to make Clinton's emails public, came the day a conservative watchdog group, Judicial Watch, made public a batch of Clinton's emails obtained through a lawsuit.
Judicial Watch said the emails showed donors to the Clinton family's charitable foundation seeking access to her during the period she was secretary of state.
Toner said the State Department believed there was "no impropriety" in foundation officials seeking to meet Clinton, saying any secretary of state or aides get such requests from a wide range of people.
The 14,900 documents referred to by Boasberg are believed to include emails not included among those Clinton previously turned over to the State Department after her use of a private email server and private email account became public.
"This number reflects both non-record (meaning personal) and record materials (meaning work related)," said a U.S. official who spoke on condition of anonymity.
Some of the emails were found on the servers of people with whom Clinton or her staff was communicating.
'Trying to pin it on me'
Former Secretary of State Colin Powell dismissed reports over the weekend that Clinton told federal investigators that it was at his suggestion that she used a personal email account, according to a media report.
Powell, who served as the nation's top diplomat from 2001 to 2005 under Republican President George W. Bush, told People magazine that while he did send Clinton a memo about his own email practices, Clinton had already chosen to use personal email rather than a government account while she had the job.
"Her people have been trying to pin it on me. ... The truth is, she was using (the private email server) for a year before I sent her a memo telling her what I did," Powell told People on Saturday.
The New York Times reported last week that Clinton told federal investigators that Powell had suggested she use personal email for unclassified email when the two spoke over dinner. The conversation occurred "in the early months" of Clinton's tenure at the State Department, the Times said, citing a forthcoming book by journalist Joe Conason that first reported the dinner exchange.
Representatives for Powell, in a separate statement to NBC News, said he had no recollection of the conversation with Clinton.
"He did write former Secretary Clinton an email memo describing his use of his personal AOL email account for unclassified messages and how it vastly improved communications within the State Department," his office told NBC on Friday.
The email exchange occurred in 2009, according to the Times.
Powell and aides to his successor as secretary of state in the Bush administration, Condoleezza Rice, received some classified information via personal email accounts, Reuters has reported. Clinton's additional use of a personal computer server at her home, however, broke State Department rules, an internal watchdog found.