Sunderland is a small, rural community located in Calvert County, Maryland, approximately 5 miles south of Dunkirk, Maryland and 10 miles north of Prince Frederick, Maryland. Although Sunderland is not incorporated and does not have a central business district, it does have a zip code, 20689. However, as of November 2007, the former Sunderland post office had closed its doors due to a lease dispute without opening a new location, and postal officials are determining where to locate a new post office location..