Grays Harbor County is a county located in the U.S. state of Washington. As of the 2010 census, the population was 72,797. The county seat is Montesano, and its largest city is Aberdeen. The county is named after a large estuarine bay near its southwestern corner.
On May 7, 1792, Boston fur trader Robert Gray crossed the bar into the bay he called Bullfinch Harbor, but which later cartographers would label Chehalis Bay, and then Grays Harbor.
The county, originally named Chehalis County, was formed out of Thurston County on April 14, 1854. The name was subsequently changed to Grays Harbor County by the Washington legislature, effective June 9, 1915. The name change helped eliminate confusion resulting from the fact that the city named Chehalis was in Lewis County.
According to the U.S. Census Bureau, the county has a total area of 2,224 square miles (5,760 km2), of which 1,902 square miles (4,930 km2) is land and 322 square miles (830 km2) (14%) is water.