In 1826 Shepard Cary opened a small store in his father's house in what was then Houlton Plantation. In 1828, the U.S. Army built the Hancock Barracks just up the hill from his store. Shepard and his father were involved in the construction of the fort and Cary became one of its principal suppliers.

Shepard became sutler to the barracks in 1837, a position he held until 1841. A sutler was an important aspect of such a northern and isolated military outpost like Hancock Barracks, they supplied all non-military items that the men and officers could not get elsewhere typically, tobacco, coffee, and sugar. Sutlers often ending up with a monopoly on the items they sold.

Shepard went on to operate one of the largest woods operations in northern Maine as well as becoming a prestigious Maine political leader.