He settled along the River Raisin in Michigan Territory in 1800,[1] became an American citizen, and engaged in trade as an employee of the North West Fur Company.

[3] He was unanimously chosen as captain of his company in April 1812,[3][4] just prior to the outbreak of the War of 1812, and since he lived quite a ways upriver, Territorial Governor William Hull asked him to move closer to the mouth of the river.

While his company built Hull's Trace to Fort Detroit[5] he began construction of a new house along the river within the boundaries of present-day Monroe, Michigan that spring.

To avoid upsetting their ally, the British took Lacroix out of Detroit secretly by boat[2] and held him on a prison ship near Fort Malden, Ontario, to await transport back to Quebec.

[3][4] When the government of the Territory of Michigan was restructured to include a new legislative council, Lacroix was one of the top 18 vote-earners in a general election.