Joint Base Lewis-McChord was created by merging Army base Fort Lewis and McChord Air Force Base in 2010.

What is now JBLM started as Camp Lewis in 1917, when the US entered World War One. Local Tacoma citizens passed a bond for two million dollars (it would be thirty-six million in today's dollars), bought seventy thousand acres, and donated the land to the Army to be used as a permanent post. This was the first outright donation of land to the US military to build a post.

The original camp was constructed in only 90 days and training of the 91st Division, originally made up of Washington State volunteers, and other units commenced immediately. At the end of the war, activity at the camp dropped drastically, to the point where local calls for the land to be returned to Tacoma for breach of contract. Funding was found, and Camp Lewis was re-designated Fort Lewis in 1927, with new units assigned there.

In the 1930s the fort expanded, adding housing and an airfield, until the end of the '30s, when the threat of war loomed, and the garrison increased from about 5,000 to 37,000 troops in three years. To accommodate these soldiers expanded rapidly, adding even more housing and training facilities, creating the North Fort complex.

When World War Two broke out the fort became very busy in the war. As the primary Army training center of the Pacific Northwest, JBLM activated, trained, and deployed six infantry divisions and assorted other battalions and smaller units over the course of the war. The base also added the Rainier Training Area, another eighteen thousand acres south of the Nisqually River, '43, and Madigan Army Medical Center '44. From 1942 to 1946, the Fort was also the site of a camp for German POWs, who were kept occupied with work details and recreation.

With the end of the war the base's activity dropped again, but the Cold War brought activity back up again within a few years. JBLM has a vital strategic position in the Northwest, well situated for defense or deployment to east Asia, and JBLM has been at the forefront of shipping troops to the Korean War, Vietnam War, Gulf War, and the Iraq and Afghanistan wars. Since 1981 JBLM has been HQ for I Corps. Following this, the 1st Special Forces group was activated in 1984, the 35th Air Defense Artillery Brigade in 1985, and the 66th Aviation Brigade and the 201st Military Intelligence Brigade in 1987. The 1990's saw the activation of the 1st Personnel Group at Fort Lewis, as well as the 555th Engineer Group and the 210th Field Artillery Brigade.

McChord Field started as Tacoma Field, the Army Airfield for Fort Lewis. It gained the name "McChord" in 1938, after Colonel William Caldwell McChord, Army pilot deceased in 1937. McChord Field flew antisubmarine patrol missions in the war, including defensive bombings of a Japanese submarine off the mouth of the Columbia River. McChord also performed most of the bombing training of the region, and units from this field deployed to all US theaters.

In the Cold War McChord-based interception units were positioned to halt expected Soviet bomber attacks from the north. Troop carrier airlift units and bomber squadrons were also stationed at McChord, right next to troops who would be deployed. This mission was performed in the Korean War. The 1960s and 1970s saw a general conversion to an airlift mission, with most of the other missions reassigned elsewhere. Since then McChord has performed many carrier missions, including deployments and humanitarian evacuations.

Presently, as a result of the 2005 BRAC commission, Fort Lewis and McChord AFB were re-merged to became a Joint Base in 2010. The base continues to serve as a training and mobilization center for all services.