Natchez is the only city in and the county seat of Adams County, Mississippi, United States. The population was 14,520 at the 2020 ce…Natchez is the only city in and the county seat of Adams County, Mississippi, United States. The population was 14,520 at the 2020 census. Located on the Mississippi River across from Vidalia, Louisiana, Natchez was a prominent city in the antebellum years, a center of cotton planters and Mississippi River trade.