Washington County is a county located in the western part of the U.S. state of Maryland. As of the 2010 census, the population was 147,430. Its county seat is Hagerstown. Washington County was the first county in the United States to be named for the Revolutionary War general (and later President) George Washington. Washington County is one of three Maryland counties recognized by the Appalachian Regional Commission as being part of Appalachia.The county borders southern Pennsylvania to the north, Northern Virginia to the south, and the Eastern Panhandle of West Virginia to the south and west.Washington County is included in the Hagerstown-Martinsburg, MD-WV Metropolitan Statistical Area, which is also included in the Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area.