On March 28, 1781, Washington County was created by an act of the Pennsylvania General Assembly, and named in honor of General George Washington. Carved from the western section of Westmoreland County, it was formed to allow the inhabitants of the area west of the Monongahela River to have more convenient courts and public offices, rather than the inconvenience and hardship of being so far remote from the seat of justice.
The town of Basset, later renamed Washington, served as the site of the first County Courthouse, a log structure built in 1787. The present day Washington County Courthouse, completed in 1900 by the F. J. Osterling Company of Pittsburgh, is registered as a national landmark.