Annual precipitation in the middle Chehalis basin ranges from 45 inches to 60 inches, increasing with elevation and from east to west. The majority of the precipitation falls as rain, with short-lived snow packs common only at higher elevations. Using 1990 U.S. Bureau of Census data and maps for the area, and relating census block numbers to the watershed boundary of the Middle Chehalis basin, the subbasin population appears to be 13,000. Based upon an average for the entire Chehalis River Basin of 2.29 people per household, there are close to 5,800 households in this subbasin. The primary land use in this region is commercial forestry in the uplands and agriculture along the Chehalis River and the lower reaches of the tributaries.
Population densities are low.
Rochester is the largest unincorporated town in the middle Chehalis basin. Other areas of residential development include Oakville, Malone, Cedarville and Porter. Low density, rural residential development is scattered along the main river. Generally, all residential and commercial development is restricted to the main river valley and along the lower reaches of major tributaries. No residences are located on the land presently being managed for timber production.