In 1855, parts of Nash, Edgecombe, Johnston, and Wayne Counties were combined to form Wilson County, North Carolina. Geography. According to the U.S. Census Bureau, the county has a total area of 543 square miles (1,410 km 2), of which 540 square miles (1,400 km 2) is land and 2.4 square miles (6.2 km 2) (0.4%) is covered by water.