[3]: 1 It first appears in historical documents in a letter of June, 1755 from Governor Robert Hunter Morris to General Braddock, in which Morris proposes using the mill to store supplies for Braddock's upcoming expedition: "Mr. Peters, who in his Way from the Camp came through Cumberland County, judges that a Place called McDowell's Mill, situate upon the new Road about twenty Miles Westward of Shippensburg, is much more convenient for the Magazine than Shippensburg."

Following the attacks at Penn's Creek, Great Cove, and Gnadenhütten in late 1755, however, local settlers decided to fortify the mill themselves.

William Maxwell (a survivor of the Braddock Expedition) formed a company of militia at Peters Township and began construction of the stockade on November 3 1755.

[5]: 425–26 On February 29 1756, a war party of eighty Lenape warriors led by Shingas and Captain Jacobs attacked the mill but were driven off by a party of forty-six men from Peters Township and by a detachment (a hundred men from Conrad Weiser's 1st Battalion[5]: 371, 446 ) under Captain John Potter, who by now had taken command of the fort.

[12] Captain John Potter, commander at McDowell's Mill, was criticized for not responding sooner to these attacks, and the local populace demanded military protection.

[5]: 430 Sporadic attacks on settlements in Franklin County continued through the summer, and the capture of Fort Granville on July 31 led many settlers to flee.

[14]: 399  Colonel Armstrong wrote to the governor that "this misfortune is happen'd thro' the weakness of the Garrison," arguing that a larger fort would protect the populace more effectively.

[5]: 434 The destruction of Kittanning relieved some of the pressure on provincial forces, and in December 1756 construction was initiated on Fort Loudoun, a formal military base about two miles north,[15] intended to replace McDowell's Mill.

In July 1763, Colonel Henry Bouquet wrote to Governor James Hamilton suggesting that McDowell's Mill be refurbished, but no action was taken.