The United States Penitentiary, Atwater is a high-security United States federal prison for male inmates in unincorporated Merced County, California. The institution also includes a minimum-security satellite camp. It is operated by the Federal Bureau of Prisons, a division of the United States Department of Justice. USP Atwater is located on land formerly part of Castle Air Force Base. It is near the city of Atwater in Merced County, California, 130 miles from San Francisco.