Cosmopolis is a city in Grays Harbor County, Washington, United States. The population was 1,638 at the 2020 census. It lies on the Chehalis River and U.S. Route 101, immediately southeast of Aberdeen. Cosmopolis historically had an economy that centered around its pulp mill, which closed in 2006.
History
The area around the mouth of the Chehalis River is the ancestral home of indigenous Coast Salish peoples who are today referred to as the Lower Chehalis. The first white settler in the area, James Pilkington, staked a Donation Land Act claim to on the south bank of the river in 1852. The site was later used for unsuccessful negotiations between indigenous representatives and the Washington territorial government for the 1855 Chehalis River Treaty. Pilkington built a cabin on the land, but later sold the property in 1853 to Kentucky-born emigrants David F. Byles and Austin E. Young. Byles and Young proposed a plat for a town named Cosmopolis on the south bank of the Chehalis River. The origin of the name is unclear; one account is that it came from an indigenous chief's name, and another claims that an earlier settler asked for a name that means "city of the whole world".
Cosmopolis was platted in 1861 and is considered the oldest modern settlement in Grays Harbor County (then known as Chehalis County). Mill Creek, a short tributary of the Chehalis River, runs through the western part of the city. The city borders Aberdeen to the northwest.
Climate
This region experiences warm (but not hot) and dry summers, with no average monthly temperatures above . According to the Köppen Climate Classification system, Cosmopolis has a warm-summer Mediterranean climate, abbreviated "Csb" on climate maps.