The patrol says 28-year-old Reymon B. Tolentino of Niles, Ill., died at a hospital after the crash Thursday.
The State Patrol said another soldier was seriously injured.
Tolentino was serving on the company's rear detachment at JBLM while most of the unit was deployed to Afghanistan. On the night of the accident he was facilitating transportation of soldiers returning home from deployment. He had not deployed in support of Operation Enduring Freedom.
"Our thoughts and prayers go out to Pvt. Tolentino's family and friends in the midst of this tragedy," said Lt. Col. Douglas Brown, commander, 14th Eng. Bn. "Our focus now is on caring for the injured and supporting the Soldiers' loved ones."
The cause of the crash is under investigation. Trooper Guy Gill said the civilian driver lost control of the 24-seat vehicle and hit a concrete barrier, knocking over a light pole.