While protecting both the watermill constructed of stone and the lighthouse built along the Lacolle River, the blockhouse was used as a military outpost by the British Army on assignment in the region of Le Haut-Richelieu Regional County Municipality and on Lake Champlain.

[4] The Lacolle Mills Blockhouse is a timber framed square two-storey structure.

[5] The blockhouse's architecture was typical of a small defensive military structure in the area not requiring significant experience to construct.

The Battle of Lacolle Mills (1812) was a short engagement in which a small garrison of Canadien Militia, with the assistance of Kahnawake Mohawk warriors, defended the Lacolle Mills Blockhouse from an American invasion force led by Major General Henry Dearborn.

[6] In the Battle of Lacolle Mills (1814) a garrison of 80 men of the 13th Regiment of Foot and a Congreve rocket detachment of the Royal Marine Artillery, later reinforced by a company of the Canadian Voltigeurs and the Grenadier company of the Canadian Regiment of Fencible Infantry successfully defended the blockhouse and stone watermill from an attacking American force of 4,000 men led by Major General James Wilkinson.