Washington County is a county located in the U.S. state of Vermont. Named after George Washington, its county seat is the city of Montpelier (the least populous state capital in the United States) and the most populous city is the city of Barre. As of the 2020 census, the population was 59,807, making it the third-most populous county in Vermont, but the third-least populous capital county in the United States after Hughes County, South Dakota and Franklin County, Kentucky; in 2023, the estimated population was 60,142. Washington County comprises the Barre, Vermont micropolitan statistical area. In 2010, the center of population of Vermont was located in Washington County, in the town of Warren.