Carthage is a city in Jasper County, Missouri, United States. The population was 15,522 as of the 2020 census. It is the county seat of …Carthage is a city in Jasper County, Missouri, United States. The population was 15,522 as of the 2020 census. It is the county seat of Jasper County and is nicknamed "America's Maple Leaf City." Jasper County was formed in 1841. Carthage was chosen as the county seat, the area cleared and the town platted in 1842. The city was named after the ancient city-state of Carthage, one of the Roman Republic's main rivals. By the time of the American Civil War, there were over 500 residents, a brick and stone courthouse, and several businesses.