Congress had ordered the Continental Army to disband after the conclusion of the American Revolution in 1783, and General George Washington had resigned his commission as commander-in-chief.

While the bulk of the Continental Army had been disbanded by the end of 1783, Jackson's Continental Regiment, commanded by Colonel Henry Jackson and a company of artillery under Brevet Major John Doughty, had remained in service.

On June 2, 1784, Congress had reissued the disbandment order, under the principle that "standing armies in time of peace are inconsistent with the principles of republican government, dangerous to the liberties of a free people, and generally converted into destructive engines for establishing despotism."

Jackson's regiment had been disbanded later in the month and Doughty's Battery had been retained at West Point guarding artillery and ammunition.

On June 3, 1784, Congress passed a new resolution:

    Resolved, That the Secretary at War take order for forming the said troops when assembled, into one regiment, to consist of eight companies of infantry, and two of artillery, arming and equipping them in a soldier-like manner: and that he be authorized to direct their destination and operations, subject to the order of Congress, and of the Committee of the states in the recess of Congress.

Thomas Mifflin, the president of Congress, had named his former aide, Josiah Harmar, to be the commander of the new regiment, with the rank of lieutenant colonel.

Harmar was commissioned as the regiment's "lieutenant colonel commandant" on August 12, 1784.

The new regiment is used primarily to man frontier outposts and guard against native attacks.

An artillery company of the new regiment is Captain John Doughty's Company of the former 2d Continental Artillery Regiment.

In 1786, Secretary of War Henry Knox had ordered Colonel Harmar to the outpost village of Vincennes to drive away the Kentucky militia, who fled at the approach of the First American Regiment.

Colonel Harmar had left one hundred regulars under the command of Major Jean François Hamtramck to build a new fort and conduct operations deep within Indian Territory.

The First American Regiment is renamed the Regiment of Infantry on September 29, 1789.