Dunkirk is a census-designated place (CDP) in Calvert County, Maryland, United States. The population was 2,520 at the 2010 census. The climate in this area is characterized by hot, humid summers and generally mild to cool winters. According to the Köppen Climate Classification system, Dunkirk has a humid subtropical climate, abbreviated "Cfa" on climate maps. Its western border is the Patuxent River, which is also the Prince George's County line. Maryland Route 4 passes through the center of Dunkirk, leading northwest 10 miles (16 km) to Upper Marlboro and south 14 miles (23 km) to Prince Frederick, the Calvert County seat. Downtown Washington, D.C., is 25 miles (40 km) to the northwest. According to the United States Census Bureau, the Dunkirk CDP has a total area of 7.3 square miles (19.0 km2), of which 6.6 square miles (17.1 km2) is land and 0.73 square miles (1.9 km2), or 10.21%, is water.