 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 also 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.