|Kelso High School|
1904 Allen Street
|Motto||We Are Kelso|
|School district||Kelso School District|
|Number of students||1,613 (2017-18)|
|Student to teacher ratio||20.86|
|Color(s)||Royal Blue, Gold, and White|
|Athletics conference||Greater St. Helens 3A|
|Mascot||The Hilanders and Lassies|
|Yearbook||Kelso Bagpipe, formally known as the Tamahnawus|
In 1905, the first Kelso High School (then known as Washington School) classes began with the first seniors graduating in 1909. Thirteen years later, a new high school was built, known as Kelso High School, in 1922. The first year the high school was accredited by the Northwest Association of Accredited Schools was in 1927. The school was moved to its current location after a new school was built in 1970. The original Kelso High School was torn down in 1987. In 2003 the building underwent extensive renovations and additions to accommodate the district wide change from junior high (7th-9th) to middle school (6th-8th) (Huntington and Coweeman). In 2008, the 100th Kelso senior class graduated.
Kelso participates in the second-largest classification of high schools in the Washington Interscholastic Activities Association (WIAA). It competes in the four-team Greater St. Helens 3A League. Kelso has a very long history and tradition with two local rivalries across the Cowlitz River in Longview; R.A. Long and Mark Morris high schools. The football games between Kelso and RA Long are known as "The Battle of the Plaid" and have met for over 90 games.
- Football: 1983
- Boys Track: 1984
- Baseball: 1995
- Softball: 1998, 2009, 2010
- Jeff Bailey - first baseman for the Arizona Diamondbacks
- Colin Kelly - Professional football player in the Canadian Football League
- Howard Hobson - began his coaching career at Kelso High School
- Tommy Lloyd - Assistant men's basketball coach for Gonzaga University
- Trevor May - Major League Baseball pitcher for the Minnesota Twins
- David Richie - Kelso High 1992 graduate, Denver Broncos, San Francisco 49ers, and retired with Green Bay Packers
- Jason Schmidt - retired Major League Baseball pitcher Pittsburgh Pirates, San Francisco Giants, Los Angeles Dodgers
- Sid Snyder - Politician and businessman
- Connor Trinneer - Actor in Star Trek, Enterprise
- Kelso High School historical highlights. http://www.tdn.com/articles/2008/05/11/top_story/doc4826366217af0223991187.txt.
- "Kelso High School". National Center for Education Statistics. Retrieved December 1, 2019.
- "Greater St. Helens 3A Athletics, Kelso High School Athletics". Retrieved August 6, 2016.
- Northwest Association of Accredited Schools http://www.northwestaccreditation.org/schools/2008-2009%20Washington%20Accredited%20Schools.pdf. 10 September 2009.
- "WASHINGTON STATE". 3rd Street Book Exchange. Retrieved September 14, 2009.
- Washington Interscholastic Athletics Association. Tournament History: School Information.