The New York Draft Riots of 1863 were principally carried out by white, working class Irish immigrants. The riots began as a response to new draft legislation which required U.S. citizens to register for the draft, but excluded African-Americans. The riots culminated in attacks on African-Americans and the burning of a variety of public buildings.

Bernstein, Iver. The New York City Draft Riots: Their Significance for American Society and Politics in the Age of the Civil War. Fargo: Bison Books, 2010.

In 1943, white U.S. servicemen in Los Angeles attacked Mexican-Americans during the "Zoot Suit Riots."

Foley, Neil. Mexicans in the Making of America. Cambridge: Belknap Press, 2014.

There have also been a large number of strikes where violence between strikers, strike breakers and/or police escalated into rioting. This was the case in the Minneapolis Teamsters Strike of 1934 as well as the so called "Memorial Day Massacre" in Chicago in 1937.

Gilje, Paul. Rioting in America. Indianapolis: Indiana University Press, 1999.

In the 1921 Tulsa Race Riot, white residents of Tulsa, Oklahoma attacked people and property in Tulsa's predominantly African-American Greenwood district. The riot, set off by anger over a black man accused of trying to rape a white elevator operator, killed dozens if not hundreds of people and decimated Greenwood, one of the most prosperous black neighborhoods in the United States--commonly referred to at that time as "Black Wall Street." After 93 years, the neighborhood has never fully recovered. Many consider it the worst race riot in American history.

Sources: http://digital.library.okstate.edu/ENCYCLOPEDIA/ENTRIES/T/TU013.html http://www.tulsahistory.org/learn/online-exhibits/the-tulsa-race-riot/

(Edit: I can't count)