Oxon Hill is an unincorporated area and census-designated place in southern Prince George's County, Maryland, United States. Oxon Hill is a suburb of Washington, located southeast of the downtown d…Oxon Hill is an unincorporated area and census-designated place in southern Prince George's County, Maryland, United States. Oxon Hill is a suburb of Washington, located southeast of the downtown district and east of Alexandria, Virginia. It contains the new 300-acre National Harbor development on the shore of the Potomac River.