7th Battalion, District of Columbia Infantry (3 months, 1861)
"Compendium of the War of the Rebellion" by Frederick H. Dyer contains no history for this unit.
Companies in this Regiment with the Counties of Origin
Men often enlisted in a company recruited in the counties where they lived though not always. After many battles, companies might be combined because so many men were killed or wounded. However if you are unsure which company your ancestor was in, try the company recruited in his county first.