Montesano is a city in Grays Harbor County, Washington, United States. The population was 4,138 at the 2020 census. It is the county seat of Grays Harbor County.
According to Edwin Van Syckle, a portion of the present-day town of Montesano was first platted in 1870 by Samuel Henry Williams, who purchased land in what was known as Medcalf Prairie, named after the early settler William Medcalf. At about the same time, surveyor Charles Newton Byles bought a farm from Walter King on the present-day site of Montesano on April 9, 1870, and later platted three blocks on the west side of Main Street. The town of Montesano was born, but it was not incorporated until November 26, 1883, by the Washington Territorial Legislature.
Prior to that time, the name Montesano was used to refer to the homestead of Isaiah Lancaster Scammon and his wife Lorinda. They filed a 640-acre Donation Land Claim on January 15,