Fort Indiantown Gap, also referred to as "The Gap" or "FTIG", is a census-designated place and U.S. Army post primarily located in Lebanon County, Pennsylvania. A portion of the installation is located in eastern Dauphin County. 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. The installation is an active National Guard Training Center and serves as headquarters for the Pennsylvania Department of Military and Veterans Affairs and the Pennsylvania National Guard. The fort surrounds Memorial Lake State Park. It is served by the Annville, Pennsylvania post office. As of the 2010 census the population was 143 residents.

The Fort Indiantown Gap Military Reservation is protected by a full-time police force, the Fort Indiantown Gap Police Department, which enforces traffic and other state laws. The post includes 18,000 acres (73 km2), with numerous ranges and training areas for the 28th Infantry Division, the 213th Area Support Group, and the Eastern Army National Guard Aviation Training Site (EAATS), Army Aviation Support Facility (AASF) at Muir Army Airfield. The installation is also home to the Northeast Counterdrug Training Center (NCTC).