Delmar is a town in Sussex County, Delaware, United States, on the Maryland border along the Transpeninsular Line. Its motto is "The Little Town Too Big for One State. " The population was 1,597 at the 2010 census, an increase of 13.5% over the previous decade. It is part of the Seaford, Delaware Micropolitan Statistical Area and a suburb of Salisbury, MD. When added with "twin city" Delmar, Maryland, the total population of the town was 4,600 at the 2010 Census.