Statistics for occurrence #1 of “Mississippi River” in chapter 1.2 of The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 7: Prisons and Hospitals.:

...nded by fences and the enclosed barracks were filled with captives. The most important of the first class were Johnson's Island, in Sandusky Bay, Ohio; City Point, Maryland, and Rock Island, in the Mississippi River . Among the second were Camp Douglas, at Chicago, Illinois; Camp Butler, at Springfield, Illinois; Camp Morton, at Indianapolis, Indiana; Camp Chase, at Columbus, Ohio; and the Barracks, at Elmira, ...
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