Washington County is a county located in the US state of Pennsylvania. As of the 2010 census, the population was 207,820. Its county seat is Washington. The county was created on March 28, 1781, from part of Westmoreland County. Both the county and the city were named for American Revolutionary War leader George Washington, later to become the first President of the United States. It was the first county in the United States to be named in his honor.