In 1945 the post shifted gears and established separation centers to quickly discharge returning soldiers. Northeast Fort Lewis functioned as a separation center discharging 200,000 servicemen between November 1945 and February 1946.
Fort Lewis and Tacoma enthusiastically welcomed the 2nd Infantry Division following the war. The division with its impressive World War II record would train and ready for any future conflict. It was not long in coming. With the North Korean invasion of South Korea on June 25, 1950, and the American response, the 2nd Infantry "Indianhead" Division was provided more equipment and sent to Korea, arriving at Pusan on August 3, 1950. The "Second to None" division warriors fought until the end of the war.
Two regimental barracks areas were constructed during the 1950s, with permanent concrete buildings. Following the Korean War, the 2nd Infantry Division returned for a short stay and then 4th Infantry "Famous Fourth" Division called the fort home. In 1966 the 4th Infantry Division deployed to Vietnam. The post became an Army Training Center, and Replacement Center, training soldiers, sending and receiving them from the Pacific.
On May 26, 1972, the 9th Infantry Division reactivated in official ceremonies. The division launched a campaign to attract volunteers and earned distinction by being the first all-volunteer division. The division trained in fast attack and mobile infantry movement. Fort Lewis gained increasing relevance in the Pacific with the activation of I Corps on October 1, 1981. I Corps and Fort Lewis contributed substantially to Desert Shield and Desert Storm (the Gulf War) in 1990-1991.
In the 1980s and to the present the installation has undergone a massive building program. A new Madigan hospital opened in 1992. Attractive barracks have replaced the World War II temporary buildings. However, the historic buildings from the 1920s and 1930s construction have been well-preserved.
Following September 11, 2001, I Corps and Fort Lewis units assumed a significant role in the "Global War on Terrorism." Stryker Brigades, equipped with Stryker armored vehicles (named for Medal of Honor recipients Private First Class Stuart Stryker [1924-1945] and Specialist Four Robert F. Stryker [1944-1967]), demonstrated rapid deployment and effectiveness. I Corps also drew upon other Fort Lewis assets such as the Special Forces, Ranger units, Special Operations, and National Guard and Reserve units.
The 2005 Base Realignment Commission directed that Fort Lewis and the adjacent McChord Air Force Base merge. The merger was part of a nationwide movement toward joint basing, the culmination of an effort beginning in the mid-1980s to unify the separate military services and bring about more effective inter-service operations. On October 1, 2010, Fort Lewis and McChord Air Force Base became Joint Base Lewis-McChord or JBLM.