Shelbyville is a city in Addison Township, Shelby County, in the U.S. state of Indiana and is the county seat. The population was 20,067 as of th…Shelbyville is a city in Addison Township, Shelby County, in the U.S. state of Indiana and is the county seat. The population was 20,067 as of the 2020 census. In 1818, the land that would become Shelbyville was ceded to the United States by the Miami tribe in the Treaty of St. Mary's. Also in 1818, the backwoodsman Jacob Whetzel and a party cut a trail through this "New Purchase" from the Whitewater River at Laurel due west to the White River at Waverly. This trail became known as Whetzel's Trace and was the first east–west road into the New Purchase of central Indiana. Whetzel's Trace was cut just 4 miles north of site of Shelbyville and proved important in the settlement of Shelby County.