This decision alienated him from his elder brother Nicholas who sided with the new Continental Congress and he was sorely tested by social ostracism.
He participated in the expedition as overseer of boats, and he and Captain Rouville of the Canadians successfully broke up the Patriots' blockade of Wood Creek.
His wife, Mary, applied for permission to join him in his new country but New York Governor George Clinton refused, saying that no Loyalist women or children would be permitted to leave until the captives taken by Butler and Brant in their raids had been returned.
Despite an inauspicious start, where he hired the wrong people for the job and allegedly spoke too familiarly with an American prisoner regarding affairs of state, it was reported that he rendered good service.
Captain Herkimer and his family settled at Cataraqui (modern Kingston, Ontario) in the mid-1780s and served in the Frontenac Militia.