Hillary Clinton speaks to voters after a town hall in Iowa City, Iowa on Dec. 16. (Melina Mara/The Washington Post)

The State Department on New Year's Eve released thousands of pages of emails sent and received by Hillary Clinton while she was secretary of state, but still fell short of the number that a federal judge ordered should be made public by the end of the year.

The State Department is releasing about 55,000 pages of correspondence from Clinton's 2009 to 2013 tenure as secretary under a court order, after Vice News reporter Jason Leopold sued the department for failing to promptly respond to a public records response for the emails, among other records. Under the process outlined by the court, the State Department was required to release emails from the Democratic presidential front-runner every 30 days, starting at the end of June. It is required to make all 55,000 pages public by the end of January. The court set targets for each month's release.

On Thursday, the department released 5,500 pages of emails — thousands short of the number necessary to meet the court's order that the department release 82 percent of the emails by the end of the year. State Department officials said they plan to release more emails next week to make up for the shortfall.

"We have worked diligently to come as close to the goal as possible, but with the large number of documents involved and the holiday schedule we have not met the goal this month," the department said in a release.

The emails released Thursday include 275 notes that have been withheld in all or part because they include material deemed classified by State Department reviewers preparing the documents for public release, a state department official said. The official indicated that most were classified at the "confidential" level, the lowest level of classification but two were classified as "secret," the higher classification level.

In all, 1,274 of Clinton's emails have now been deemed too secret for public release. The mounting number of correspondence with classified material has been a lingering problem for Clinton on the presidential campaign, spotlighting her decision to exclusively use a private email account, routed through a personal server installed at her suburban New York home, for work related correspondence while secretary of state. Clinton has said none were marked classified at the time they were sent. She and State Department officials have characterized the material has having been "upgraded" to a classified level through the review process. It is the responsibility of individual government officials to properly handle classified material. Officials are also required to avoid including the material in insecure email, and to properly mark it as classified.

Clinton turned over the records to the State Department in December 2014, nearly two years after leaving office, in response to a request from the department. State Department officials had realized the agency had gaps in its records after finding it did not have full access to her correspondence while preparing to submit documents to the congressional committee investigating the 2012 attacks on U.S. installations in Benghazi, Libya.

[State Department's account of email request differs from Clinton's]

She has said her lawyers reviewed the documents and gave the State Department more than 30,000 emails that were potentially work-related. She has said she chose not to keep 31,000 that her lawyers deemed purely personal.

The FBI has been probing the security of Clinton's private server, which was turned over to investigators in August by a Denver company that had managed the device since Clinton left office. The State Department's inspector general has also been reviewing her email practices.

[FBI looking into the security of Clinton's email server]

At a lengthy appearance before a House special committee on Benghazi in October, Clinton indicated that email was not her primary mode of communication while secretary. That has been borne out in the thousands of pages of emails released by the State Department so far, which have consisted primarily of email chains and press accounts forwarded to Clinton by her top aides. Responses from Clinton were often terse -- often a quick direction for a staffer to call her or to print a particular document. Still, the correspondence has provided a unique window into the day-to-day doings of Clinton's time as the nation's top diplomat.

In the emails released most recently, for instance, Clinton thanked a top aide, Joe McManus, in July 2012 for forwarding what appeared to be information about a threat against her long-serving close personal aide, Huma Abedin.

"Thanks for the update and for the peace of mind from the NYPD," Clinton wrote as part of an email chain titled "Huma" and that included the State Department's top security officer, Eric Bosworth. Abedin's primary residence with her husband, former Rep. Anthony Weiner, was in Manhattan.

The emails released Thursday also contain some new communications between Clinton and longtime friend and former aide Sidney Blumenthal. Republicans have objected to the access Blumenthal had to the secretary of state.

In late June 2010, just after publication of a damning article about Gen. Stanley McChrystal, then the commanding general in Afghanistan, Blumenthal sent her a note gaming out whether McChrystal would or should keep his job.

"McChrystal retained becomes the indispensable man; Obama becomes his hostage," Blumenthal wrote. "McChrystal rebuked will be silent in the future, but the Afghanistan operation will be personalized: McChrystal will become the crucial theoretician, general, and receive either credit or blame."

President Obama sacked the general that same week, after summoning him to the Oval Office.

Some email communications were both personal and political. On May 12, 2012, Clinton received a note informing her that George Soros, the billionaire philanthropist and donor, regretted supporting Barack Obama in the 2008 presidential primaries when Clinton was a candidate. "He said he's been impressed that he can always call/meet with you on an issue of policy and said he hasn't met with the President ever ....He then said he regretted his decision in the primary." wrote Neera Tanden, president of the Center for American Progress and a veteran of Clinton's 2008 presidential campaign. Tanden emailed the secretary the day after she sat next to Soros at a dinner sponsored by the Democracy Alliance, a group of leading donors to liberal causes and Democratic candidates

Carol Morello, Anne Gearan, Tom Hamburger, Mary Jordan, Carol D. Leonnig, Karen Tumulty and Vanessa Williams contributed to this report.

This item has been updated.