The release marks the culmination of a nearly two-decade project to release information on violence and disappearances of dissenters after a 1976 coup that installed the dictatorship, which the United States initially supported.
"As the families of victims continue their quests for truth and justice, the declassification of these records helps confront the past with honesty and transparency," the U.S. Department of State said in a statement on Friday.
The data release adds more than 5,600 new documents and almost doubles the trove released previously in 2002 and over the last few years, the statement said.
The declassification effort has included records from U.S. law enforcement agencies, the Department of Defense, the Department of State and the presidential libraries at the National Archives.
The move is part of long-running effort by various U.S. administrations to help smooth relations in Latin America that had been affected by Washington's backing of former military dictatorships in the region.U.S. Secretary of State Mike Pompeo is on a tour of South American countries, but is not expected to visit Argentina. The U.S. archivist will present the new records to Argentine officials on Friday.