The 1st Marine Regiment is an infantry regiment

Regiment

A regiment is a major tactical military unit, composed of variable numbers of batteries, squadrons or battalions, commanded by a colonel or lieutenant colonel...

 of the United States Marine Corps

United States Marine Corps

The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...

 based at Marine Corps Base Camp Pendleton

Marine Corps Base Camp Pendleton

Marine Corps Base Camp Pendleton is the major West Coast base of the United States Marine Corps and serves as its prime amphibious training base...

, California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. The regiment, sometimes known as "Inchon", falls under the command of the 1st Marine Division and the I Marine Expeditionary Force.
The Regiment comprises four infantry

Infantry

Infantrymen are soldiers who are specifically trained for the role of fighting on foot to engage the enemy face to face and have historically borne the brunt of the casualties of combat in wars. As the oldest branch of combat arms, they are the backbone of armies...

 battalion

Battalion

A battalion is a military unit of around 300–1,200 soldiers usually consisting of between two and seven companies and typically commanded by either a Lieutenant Colonel or a Colonel...

s and one headquarters company:

• Headquarters Company 1st Marines (HQ/1)
• 1st Battalion 1st Marines
  1st Battalion 1st Marines
  1st Battalion 1st Marines is an infantry battalion in the United States Marine Corps based out of Camp Pendleton, California consisting of anywhere from 800 to 2,000 Marines and Sailors, but the number fluctuates depending on the Battalion's mission...
  
   (1/1)
• 2nd Battalion 1st Marines
  2nd Battalion 1st Marines
  2nd Battalion, 1st Marines is an infantry battalion in the United States Marine Corps based out of Marine Corps Base Camp Pendleton, California. Nicknamed "The Professionals," the battalion consists of approximately 1000 Marines and Sailors...
  
   (2/1)
• 3rd Battalion 1st Marines
  3rd Battalion 1st Marines
  3rd Battalion 1st Marines is an infantry battalion in the United States Marine Corps based out of Camp Horno on Marine Corps Base Camp Pendleton, California...
  
   (3/1)
• 1st Battalion 4th Marines
  1st Battalion 4th Marines
  1st Battalion, 4th Marines is an infantry battalion in the United States Marine Corps based out of Marine Corps Base Camp Pendleton, California consisting of approximately 1000 Marines and sailors...
  
   (1/4) - (assigned to the 1st Marine Regiment for historical reasons)

The 1st Marines were activated in Philadelphia, Pennsylvania

Philadelphia, Pennsylvania

Philadelphia is the largest city in the Commonwealth of Pennsylvania and the county seat of Philadelphia County, with which it is coterminous. The city is located in the Northeastern United States along the Delaware and Schuylkill rivers. It is the fifth-most-populous city in the United States,...

 on November 27, 1913.