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is a city in Grays Harbor County, Washington, United States. The population was 3,312 at the 2000 census. It is the county seat of Grays Harbor County.
Montesano is located at (46.985865, -123.597726). It is on the north slope of the Chehalis River valley, near the confluence of the Wynoochee River and Chehalis River. The town is bordered on the North and west by Lake Sylvia and Sylvia Creek.
According to the United States Census Bureau, the city has a total area of 10.4 square miles (27.0 km²), of which, 10.3 square miles (26.8 km²) of it is land and 0.1 square miles (0.2 km²) of it (0.86%) is water.