Natchez, officially the City of Natchez, is the only city in and the county seat of Adams County, Mississippi, United States. The population wa…Natchez, officially the City of 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 in Concordia Parish, Louisiana, Natchez was a prominent city in the antebellum years, a center of cotton planters and Mississippi River trade.