The Infantry Branch is a branch of the United States Army first established in 1775.

Ten companies of riflemen were authorized by a resolution of the Continental Congress on 14 June 1775. However, the oldest Regular Army infantry regiment, the 3rd Infantry Regiment, was constituted on 3 June 1784, as the First American Regiment.

On 3 March 1791, Congress added to the Army "The Second Regiment of Infantry"

The Army organized into seven infantry regiments, 1821;

Ten one-year regiments were authorized by an Act of Congress on 11 February 1847 because of the Mexican–American War, but only the 9th through 16th Infantry Regiments were activated; they did not re-form permanently until the 1850s and 1860s.

Civil War expansion to 19 regiments;

In a major expansion under General Order 92, War Department, 23 November 1866, pursuant to an act of Congress of 28 July 1866 (14 Stat. 332), the 2nd and 3rd battalions of the existing 11th through 19th Infantry Regiments were expanded and designated as the 20th through 37th Infantry Regiments. Four new regiments (the 38th through 41st) were to be composed of black enlisted men, and the new 42nd through 45th Infantry Regiments for wounded veterans of the Civil War.

This was reduced by consolidation to 25 regiments under General Order 17, War Department, 15 March 1869, with the 24th and 25th Infantry Regiments constituting the black enlisted force. On 2 February 1901, Congress passed the Army Reorganization Act, which authorized five additional regiments, the 26th through 30th;