Chicago's most famous race riot . . .occurred between July 27 and August 3, 1919. The violence was precipitated by the drowning of an African American teenager who had crossed an invisible line at 29th Street separating customarily segregated “white” and “black” beaches. Soon, white and black Chicagoans, especially in the South Side residential areas surrounding the stockyards, engaged in a seven-day orgy of shootings, arsons, and beatings that resulted in the deaths of 15 whites and 23 blacks with an additional 537 injured (342 black, 195 white). The police force, owing both to understaffing and the open sympathy of many officers with the white rioters, was ineffective; only the long-delayed intervention of the state militia brought the violence to a halt, and heavenly intervention in the form of rain was probably an important factor as well. The passions of this outbreak were rooted in pent-up tensions surrounding the massive migration of southern blacks during World War I: sometimes hired as strikebreakers, their increased industrial presence was viewed by many white workers as a threat to their own livelihoods, fueling attempts to impose rigid physical boundaries beyond which blacks could not penetrate. — Steven Essig, Encyclopedia of Chicago

Contemporary Accounts and Reports:

Deaths, Disturbances, Disasters, and Disorders in Chicago, a site at the Chicago Public Library, contains the Cook County Coroner's Report, The Race Riots: Biennial Report 1918-1919 and Official Record of Inquests on the Victims of the Race Riots of July and August, 1919, Whereby Fifteen White Men and Twenty-three Colored Men Lost Their Lives and Several Hundred Were Injured. This is a key source for exactly who did what and when.

Homicide in Chicago, 1870-1930 at Northwestern University has The Negro in Chicago, the 1922 Chicago Commission on Race Relations report — downloadable in Pdf format. You need Adobe Acrobat Reader for Pdf files. This is indispensable for the facts about the riot and also for information on the Great Migration of Southern blacks to Chicago in the 1910s.

There are selected newspaper accounts at Jazz Age Chicago

Walter White, "The Causes of the Chicago Race Riot," The Crisis, XVIII (October, 1919), p. 25 — White was a long-time NAACP official; The Crisis is a NAACP publication.

Carl Sandburg, "The Chicago Race Riots" (July 1919) in the on-line Chicago Encyclopedia — Sandburg was a well-known poet and cultural and political radical

Letters from African-American migrants to Chicago at DePaul University.

Secondary Accounts (taken from Homicide in Chicago, 1870-1930):
William M. Tuttle, Jr., Race Riot – Chicago in the Red Summer of 1919, (Chicago, 1996) and see the valuable, “Essay on Sources,” pp. 269 - 289.
Dominic A. Pacyga, “Chicago’s 1919 Race Riot: Ethnicity, Class and Urban Violence,” in Raymond Mohl, ed. The Making of Urban America, (2d. Ed. 1997).
Glen E. Holt and Dominic A. Pacyga, Chicago: A Historical Guide to the Neighborhoods – The Loop and South Side, (with historical photographs) Chicago Historical Society, 1979.
Grossman, James R. Land of Hope: Chicago, Black Southerners, and the Great Migration (Chicago, 1989) This readable, scholarly account provides an extensive analysis of both the southern roots of the Great Migration and the making (and remaking) of Chicago’s black community during the early twentieth century.
U.S. Census, “Negro Population in the United States, 1790-1915,” Washington, Gov’t Printing Office, 1918. A special report of the U.S. Census.
Harold F. Gosnell, Negro Politicians, U. Chicago Press, originally published 1935, reprinted with a new Introduction by James Q. Wilson, 1967. Chronicles the activities of Negroes in politics and the society in Chicago, where Negroes first entered northern politics in significant numbers. See especially, Ch. XII, “Negro Police Officers,” p.244-279.
Spear, Allan H. Black Chicago: The Making of a Negro Ghetto, 1890-1920, (Chicago, 1967). This study emphasizes economic, demographic, and institutional conditions and chronicles the development of the city’s black community.
St. Clair Drake and Horace Clayton, Black Metropolis, (New York, 1945). Considered by many to be the most authoritative and exhaustive study of the Negro community in Chicago.