Mack moved to Detroit, Michigan in either 1800 or 1807. He left his family behind in Vermont where the children could be better schooled and established a string of merchant and business ventures in Michigan. In Detroit during the War of 1812, he was given the captaincy of a company under General William Hull; however, the city was quickly surrendered to the British. Mack is said by his sister to have broken his sword over his knee and thrown it into the lake on hearing of the surrender. To save his property, his housekeeper housed British officers and pretended the house and business were her own.