High Quality Content by WIKIPEDIA articles! The 1968 Illinois earthquake (or "New Madrid event") was the largest recorded earthquake in the U.S. Midwestern state of Illinois. Striking at 11:02 a.m. on November 9, it measured 5.4 on the Richter scale. Although there were no fatalities, the event caused considerable structural damage to buildings, including the toppling of chimneys, and shaking in the region`s largest city Chicago. The earthquake was one of the most widely felt in U.S. history, affecting 23 states over an area of 580,000 square miles (1,500,000 km2). In studying its cause, scientists discovered the Cottage Grove Fault in the Southern Illinois Basin.