He had begun fur trading and by 1790 built quite a business with his wife's help and her Odawa family connections. They were among the elite traders; they sent their sons to Montreal for their education and their daughters to Europe. Their lives were quite interrupted by the War of 1812, during which Mitchell rejoined the British Army. Afterward, under pressure by Americans against British nationals trading in the United States, the family moved across the border to Drummond Island. Mitchell lived there with three of their sons, and Elizabeth was with him temporarily. About 1816, she returned to the US with their son William to manage their holdings on Mackinac. They had retail stores at both places and traveled to see each other.