Fort Casco was built at the behest of Wabanakis who desired a convenient place to trade and repair tools, while the British sought to foster better relations with Indians and pull them away from the French sphere of influence by providing them cheaper goods.

Governor Joseph Dudley held a conference at New Casco with representatives of the Abenaki tribes on June 20, 1703 trying to convince them not to ally with the French.

His efforts were unsuccessful, as the fort was besieged only two months later by Abenaki chiefs Moxus, Wanungonet, Nescambious, and their French Allies in the Northeast Coast Campaign (1703).

Vastly outnumbered English were relieved by the armed vessel "Province Galley", which dispersed the Wabanakis and the some 500 French with its guns.

When the resettlement of present-day Portland began in 1716, the Province of Massachusetts ordered that the fort at New Casco be demolished rather than maintain it.