Kelso is a city in the southwestern part of the U.S. state of Washington and is the county seat of Cowlitz County. At the 2010 census, the population was 11,925. Kelso is part of the Longview, Washington Metropolitan Statistical Area, which has a population of 102,410.

Kelso and Longview are the home of the Cowlitz Black Bears baseball team. The Black Bears play in the West Coast League, an independent summer baseball league with teams from Washington, Oregon, and British Columbia. The team plays at David Story Field on the Lower Columbia College campus.

Within the city limits, there are eight city parks totaling 50 acres (200,000 m ²) and 6 miles (10 km) of bicycle and multi-use paths. The largest park is Tam o' Shanter Park, a multi-use park comprising 38 acres (150,000 m ²) along the Coweeman River. The facilities include multipurpose fields for soccer, three girls' fastpitch softball fields, one Babe Ruth field, five Cal Ripken baseball fields, and three basketball courts. The park hosts the annual Kelso Hilander Festival which includes Scottish Highland games. The park is named after a Scottish bonnet, the Tam o' Shanter.