Shelbyville is a city in Shelby County, Missouri, United States. The population was 518 at the 2020 census. It is the county seat of Shelb…Shelbyville is a city in Shelby County, Missouri, United States. The population was 518 at the 2020 census. It is the county seat of Shelby County. Shelbyville was platted in 1836. Like the county in which it is located, Shelbyville was named for Governor Isaac Shelby of Kentucky. A post office has been in operation at Shelbyville since 1836.