Statistics for occurrence #1 of “Washington, D. C.” in chapter 8, regiment reg15 of Frederick H. Dyer, Compendium of the War of the Rebellion: Regimental Histories:

...
Organized at Washington, D. C. , April 26, 1861, for the defence of the Capital. Mustered out July 19, 1861.
...
Max. Freq. Min. Freq.
Entity Corpus Doc Corpus Doc  

† 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.