[2] It is located adjacent to Interstate 81, 23 miles (37 km) northeast of Harrisburg, just north of the northern terminus of Pennsylvania Route 934 at I-81's Exit 85.

[3] The post includes about 18,000 acres (73 km2) of land, with numerous ranges and training areas for the Pennsylvania National Guard and other active-duty and reserve-component military units as well as law-enforcement agencies.

The installation surrounds Memorial Lake State Park and Indiantown Gap National Cemetery.

In 1975, the Secretary of the Army renamed the post Fort Indiantown Gap, in order to more closely align it with other Active Duty stations throughout the United States.

A massive construction project got underway, as 13,000 workmen quickly prepared for the arrival of troops and supplies, and the U.S. Army garrison at FTIG was born.

It was one of the nation’s busiest Army training camps, serving as the staging area for the New York Port of Embarkation.

Once Allied Forces gained a foothold in Europe, IGMR also served as a German POW compound.

[3] As World War II continued with ever increasing American involvement, a transportation corps training center was established for the purpose of educating soldiers who would later be used in port battalions.

Three dry landships: S.S. Manada, S.S. Swatara, and the S.S. Indiantown were built at IGMR and used for Army stevedore training.

[3] When the war ended, IGMR became a separation center for officers and enlisted men returning from overseas, mostly from Europe.

[3] From 1951 to 1953, during the Korean War, the Gap again had a strategic role as the home of the 5th Infantry Division, whose mission was to train 32,000 troops as replacements for assignment to Korea.

[3] During the late 1960s and early 1970s, during the Vietnam War, Fort Indiantown Gap served as one of the largest Reserve Officers' Training Corps (ROTC) summer camps for the U.S.

In 1980, the Gap again became a refugee camp when over 19,000 Cuban aliens were brought there for processing and sponsorship after the Mariel boatlift.

[6] In 1990, the Gap served as a mobilization and embarkation center for active, reserve, and guard units deploying to the first Persian Gulf War.

In the fall of 1991, the Gap served as the training center for the 84th and 85th PA State Police academy classes.

In July 1995, the Base Realignment and Closure Commission (BRAC) recommended closing Fort Indiantown Gap, except for minimum essential ranges, facilities, and training areas used by reserve components.

In 2021, EAATS was selected to be the first unit in the Army—active-duty, National Guard or Reserve—to receive a new variant of the UH-60 Black Hawk helicopter, the UH-60V.

For years an "open post," Fort Indiantown Gap began construction on the first of two access-control points, or gates, in December 2021.

Four members of the group had taken out an insurance policy on Joseph Raber, an elderly man who lived in the area, and promised to take care of him until his death.