Washington County is a county located in the western part of the US state of Maryland, bordering southern Pennsylvania to the north, northern Virginia to the south, and the Eastern Panhandle of West Virginia to the south and west. As of the 2010 Census, its population is 147,430. Washington County was the first county in the United States to be named for the Revolutionary War general (and later President) George Washington. Its county seat is Hagerstown.
Washington County is one of three counties in the Hagerstown-Martinsburg, MD-WV Metropolitan Statistical Area. Washington county has experienced a population boom, and is one of the fastest growing counties in the country, due to an influx of people from the Washington-Baltimore metropolitan areas.
The western portions of Maryland (including present Washington County) were incorporated into Prince George's County in 1696. This original county included six current counties. The first to be created was Frederick, separated from Prince George's County in 1748.
Washington County was formed on October 1, 1776 by the division of Frederick County. At the same time, Montgomery County was also separated from Frederick County and was named for General Richard Montgomery. Washington County as created included land later to become Allegany County (created in 1789) and Garrett County (included in Allegany County when it was created in 1789, but later separated from Allegany County). Washington County thus originally included the entire western part of the state.
A number of properties in the county are listed on the National Register of Historic Places.