Deputy Justin DeRosier, 29, had arrived at the scene northeast of Kalama around 10 p.m., the Cowlitz County Sheriff’s Office wrote on Facebook.
DeRosier was shot soon afterwards and received medical care. He died at a nearby hospital, officials said.
Other circumstances surrounding the shooting were unclear. The sheriff’s office announced it had found a “person of interest” in the shooting and was following leads.
“Deputy DeRosier made a huge impact in his short career and will forever live in our hearts and mind,” the sheriff’s office wrote.
Sheriff Brad Thurman told the Longview Daily News it was believed to be the first death of an officer in the line of duty in the history of the Cowlitz County Sheriff’s Office.
A 2012 graduate of Washington State University and a deputy since 2016, DeRosier is survived by his wife and young daughter.