From the overview:
The Department of State prepared this report using information from U.S. embassies and consulates abroad, foreign government officials, nongovernmental and international organizations, and published reports. The initial drafts of the individual country reports were prepared by U.S. diplomatic missions abroad, drawing on information they gathered throughout the year from a variety of sources, including government officials, jurists, the armed forces, journalists, human rights monitors, academics, and labor activists. This information gathering can be hazardous, and U.S. Foreign Service personnel regularly go to great lengths, under trying and sometimes dangerous conditions, to investigate reports of human rights abuse, monitor elections, and come to the aid of individuals at risk, such as political dissidents and human rights defenders whose rights are threatened by their governments.
Once the initial drafts of the individual country reports were completed, the Bureau of Democracy, Human Rights and Labor, in cooperation with other Department of State offices, worked to corroborate, analyze, and edit the reports, drawing on their own sources of information. These sources included reports provided by U.S. and other human rights groups, foreign government officials, representatives from the United Nations and other international and regional organizations and institutions, experts from academia, and the media. Bureau officers also consulted experts on worker rights, refugee issues, military and police topics, women's issues, and legal matters. The guiding principle was to ensure that all information was assessed objectively, thoroughly, and fairly.
The reports in this volume will be used as a resource for shaping policy, conducting diplomacy, and making assistance, training, and other resource allocations. They also will serve as a basis for the U.S. Government's cooperation with private groups to promote the observance of internationally recognized human rights.
Source: U.S. State Department
Link to report - list by country