The 1968 Illinois earthquake was the largest recorded earthquake in the U.S. Midwestern state of Illinois. Striking at 11:02 am on November 9, it measured 5.4 on the Richter scale. Although no fatalities occurred, the event caused considerable structural damage to buildings, including the toppling of chimneys and shaking in Chicago, the region's largest city. The earthquake was one of the most widely felt in U.S. history, largely affecting 23 states over an area of 580,000 sq mi (1,500,000 km2). In studying its cause, scientists discovered the Cottage Grove Fault in the Southern Illinois Basin.

Harrisburg is a city in and the county seat of Saline County, Illinois, United States. It is located about 57 miles southwest of Evansville, Indiana, and 111 mi (179 km) southeast of St. Louis, Missouri. Its 2020 population was 8,219, and the surrounding Harrisburg Township had a population of 10,037, including the city residents. Harrisburg is included in the Illinois–Indiana–Kentucky tri-state area and is the principal city in the Harrisburg micropolitan statistical area with a combined population of 24,913.