Aberdeen is a city in Monroe County, Mississippi. The population was 5,612 at the 2010 census. It is the county seat of Monroe County. Located on the banks of the Tombigbee River, Aberdeen was one of the busiest Mississippi ports of the 19th century. Cotton was heavily traded in town, and for a time Aberdeen was Mississippi's second largest city. Today Aberdeen retains many historic structures from this period, with over 200 buildings on the National Register of Historic Places.