The Northeast United States contains of 2 sub regions that accounts for 18.4% of U.S. population, New England, containing rest of Maine, New Hampshire, Massachusetts, Connecticut, Vermont and Rhode Island, and the Mid-Atlantic states with New York, Pennsylvania and New Jersey.
Or straight down to the point:
The Northeast United States contains of 2 sub regions that accounts for 18.4% of U.S. population, New England and the Mid-Atlantic states.