Harrisburg is a city and township in Saline County, Illinois, United States. The estimated 2007 population was 9,638, with a township population of 11,658. It is the county seat of Saline County. 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 was made infamous for the Ohio River flood of 1937, the old Crenshaw House (also known as the Old Slave House), and prohibition era gangster Charlie Birger. A Cairo and Vincennes Railroad boomtown, the city was one of the leading bituminous coal mining distribution hubs of the American Midwest between 1900 and 1937. At its peak, Harrisburg had a population that reached 16,000 by the early 1930s, and had one of the largest downtown districts in Southern Illinois, but it has been in severe economic decline due to the decreased demand for high sulfur coal, the removal of the New York Central railroad, and several floods leaving much area around the city unfit for residential, commercial, or industrial use. 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 26,733.