Some useful maps are found in Mississippi Maps, 1816-1873 (Jackson, Mississippi: Mississippi Department of Archives and History, 1970; Family History Library book Q 976.2 A1 No. 1).
The University of Mississippi has a large collection of maps dating from 1900. The Mississippi Department of Archives and History has a smaller collection of maps but has useful atlases and national gazetteers.
United States Census Bureau State and County Map. This map will allow you to zoom in on any state or county in the United States and read the names of all of the neighboring counties.Printable maps are also available from the National Atlas of the United States -- http://nationalatlas.gov/printable.html