The Baltimore riot of 1861 was a civil conflict on Friday, April 19, 1861, on Pratt Street, in Baltimore, Maryland. It occurred between antiwar "Copperhead" Democrats and other Southern/Confederate sympathizers on one side, and on the other, members of Massachusetts and Pennsylvania state militia regiments en route to the national capital at Washington who had been called up for federal service. The fighting began at the President Street Station, spreading throughout President Street and subsequently to Howard Street, where it ended at the Camden Street Station. The riot produced the first deaths of Union volunteers by hostile action, although caused by civilians, in the American Civil War. Civilians among the attackers also were killed.

Baltimore is the most populous city in the U.S. state of Maryland. With a population of 585,708 at the 2020 census, it is the 30th-most populous city in the United States. Baltimore was designated an independent city by the Constitution of Maryland in 1851, and is currently the most populous independent city in the nation. As of the 2020 census, the population of the Baltimore metropolitan area was 2,838,327, the 20th-largest metropolitan area in the country. When combined with the larger Washington metropolitan area, the Washington–Baltimore combined statistical area (CSA) has a 2020 U.S. census population of 9,973,383, the third-largest in the country.