Marshallberg is an unincorporated area and census-designated place in Carteret County, North Carolina, United States. As of the 2010 census it had a population of 403.Marshallberg is located east of the center of Carteret County, bounded on the east by Core Sound, on the south by The Straits, on the west by Sleepy Creek, and on the northeast by Great Marsh Creek. The community of Gloucester is to the west across Sleepy Creek. The town of Beaufort is 7 miles to the west by water and 15 miles by road.The Marshallberg CDP has a total area of 0.66 square miles, of which 0.01 square miles, or 0.97%, is water.