Statistics for occurrence #1 of “Potomac river” in chapter 1.36 of Southern Historical Society Papers, Volume 30.:

...utenant J. E. B. Stuart, U. S. regular cavalry, who was returning to Virginia, to offer his services to the Governor of the State of his birth. Breathed, two days after reaching home, crossed the Potomac river at Williamsport, Md., went to Martinsburg, Va., and joined a company of cavalry that was being organized at that place under the command of Captain John Blair Hoge, afterward Company B, First Virgini...
Max. Freq. Min. Freq.
Entity Corpus Doc Corpus Doc  
Potomac River (United States) 286 0 0 0 0 user votes
Potomac River (Maryland, United States) 2 0 0 0 0 user votes
Potomac River (Maryland, United States) 2 0 0 0 0 user votes

† This entity has been selected by the automated classifier as the most likely match in this context. It may or may not be the correct match.