eBook: The Great Chicago Fire of 1871
Chicago Historical Society: The Great Chicago Fire Includes info about pre-1871 Chicago, visuals, primary sources, maps, eyewitness sources, and more.
Encyclopedia of Chicago: The Civil War
Smithsonian: What Did Chicago Look Like Before the Great Fire?
National Geographic Education: Great Chicago Fire & Rebuilding
Curious City: What If the Great Chicago Fire of 1871 Never Happened? Interesting to think about this!