Plum Island is a populated place LOCATED WITHIN the City of Newburyport. In turn, the City of Newburyport is located within Essex County.
Plum Island is located at latitude 42.813 and longitude -70.813.
Since Plum Island is located within the City of Newburyport, all of the census and demographic data for residents of Plum Island are included as part of the information reported for City of Newburyport in the "Profile" tab above.