Thomas helped suppress Shays' Rebellion in 1786, which earned him the rank of major. In the years following, he witnessed and was offended by the continuing persecution of Loyalists in Massachusetts. He realized that in the depressed economic conditions that followed the Revolutionary War, and with his own deep debts, he was unlikely to see his former prosperity again. In 1793, Thomas met in New York City with Mohawk leader Joseph Brant, who offered to show him the best land for settlement in Upper Canada, where the Crown was encouraging development. He and four associates travelled to Upper Canada to petition Lieutenant Governor John Simcoe for a land grant. They received in the Thames Valley, and founded Oxford-on-the-Thames (later known as Ingersoll, Ontario), on condition that they populate it with forty other families within seven years. After winding up their affairs in Great Barrington, the Ingersoll family moved to Upper Canada in 1795.