The Army will deactivate the 4th Stryker Brigade, which has about 4,000 soldiers, including 1,000 remaining in Afghanistan who are due back this summer, said spokesman Lt. Col. Gary Dangerfield.
JBLM currently has a total of 33,645 active duty soldiers, Dangerfield said. Including Air Force and reservists, the total military population is close to 40,000 he said.
As part of the Army reorganization, some combat soldiers will be added to brigades.
Army officials assured U.S. Rep. Denny Heck that Lewis-McChord still has a significant mission.
"Today's announcement ensures that Joint Base Lewis-McChord will retain its status as the U.S. Army's main West Coast force projection base. The base will continue to play an important role in the decades ahead as our national security strategy pivots to the Asia-Pacific region," Heck, a Democrat, said.
Sen. Patty Murray, D-Wash., said she was disappointed in the reductions at JBLM but said it will remain "one of the premier military installations in America."
"In the coming months, I will continue working closely with JBLM leaderships, community partners in the south Sound, and all those directly affected to make this transition as seamless as possible," she said in a statement.
The base near Tacoma is one of 10 in the United States losing brigades in a reorganization announced by Army Chief of Staff Gen. Ray Odierno to reduce troop strength by 80,000 to 490,000.
"We hate to lose anything, to be honest with you," said spokesman Dangerfield at JBLM. "It can have an impact on the organization. We will make the adjustment."
The force at JBLM will be reduced as soldiers are reassigned or their service time expires.
"We don't lay people off," Dangerfield said.
It won't affect JBLM's readiness, he said.
"Our new mission now is to focus on the Pacific and we can more than meet that challenge if it comes down to the scenario, and we can be augmented," Dangerfield said.
Some civilian jobs will be impacted and the effect on surrounding communities of Lakewood, Lacey and DuPont remains to be seen.
After the deactivation of the 4th Stryker Brigade, there will be two Stryker brigades - the 2nd and 3rd - at the base that pioneered the use of the eight-wheeled Stryker vehicles and first sent them into battle in Iraq.
The 4th Stryker Brigade deployed twice to Iraq in addition to its current Afghanistan mission. It was the last combat brigade in Iraq in August 2010.