Kelso, city (1990 pop. 11,820), seat of Cowlitz co., SW Wash., on the Cowlitz River near the Columbia, in a fertile farm area; inc. 1889. Boatbuilding, fishing, and dairy farming are the major industries. Machinery and paper and wood products are manufactured. Settled in 1847, Kelso was an important stopping place for early steamboat travel along the Cowlitz River.