The Baltimore Know-Nothing riots of 1856 occurred in Baltimore, Maryland between September and November of that year. The Know-Nothing Party gained traction in Baltimore as native-born residents disliked the growing immigrant population. Local street gangs became divided on political grounds, with the Know-Nothing affiliated gangs clashing with gangs affiliated with the Democratic Party. The partisans were involved in widespread violence at the polls and across Baltimore during municipal and national elections that year.

The Know Nothings were a nativist political movement in the United States in the 1850s, officially known as the Native American Party before 1855, and afterwards simply the American Party. Members of the movement were required to say "I know nothing" whenever they were asked about its specifics by outsiders, providing the group with its colloquial name.