Eighty-one messages were classified, mostly at the lowest level of sensitivity. None was declared top secret.
The department has now released more than 45,000 pages of emails from the private account Clinton used as secretary of state.
It plans to finish making her emails public on February 29, a day before the critical Super Tuesday primaries when multiple states hold nominating contests .
Clinton has struggled to put the email controversy to rest as she seeks the Democratic presidential nomination.
Last month, 22 emails were withheld in full because they contained "top secret" material. The FBI also is examining the security of the home server she maintained for email use while in office.