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 miles southeast of St. Louis, Missouri. The 2010 population was 9,017, and the surrounding Harrisburg Township had a population of 10,790, 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.Located at the concurrency of U.S. Route 45, Illinois Route 13, Illinois Route 145, and Illinois Route 34, Harrisburg is known as the "Gateway to the Shawnee National Forest", and is also known for the Ohio River flood of 1937, the old Crenshaw House, the Tuttle Bottoms Monster, prohibition-era gangster Charlie Birger, and the 2012 EF4 tornado.