Cornwall County was a county of the former Province of New York, established on September 5, 1665 from 25,100 square miles (65,000 km2) of land that had been granted to the Duke of York in modern Maine. As established, the grant ran all the way from the St. Lawrence River to the Atlantic Ocean, between the Kennebec and St. Croix rivers, and produced what today is most of Aroostook, Piscataquis, Washington, Hancock, Penobscot, Waldo, Knox, Lincoln, Kennebec, Somerset, and Sagadahoc Counties.
On October 7, 1673, Massachusetts, relying on a new survey of its northern border, and responding to the Dutch capture of New York in August 1673 as a result of the Third Anglo-Dutch War, claimed 200 square miles (500 km2) of the Duke of York’s territory east of the Kennebec River in present day Maine, including the Pemaquid settlement, and established a new county there. On May 27, 1674, this county was named Devonshire. Cornwall was implicitly reduced to the area north of the Massachusetts claim. Cornwall and Devonshire were lost to the Abnaki Indians in a war in the Autumn of 1675. Cornwall County was recreated on November 1, 1683, conforming to the original grant, still part of New York. Cornwall continued unchanged until the Spring of 1687, when it was transferred to the expanded Dominion of New England, extinguishing New York’s claim to the land. Cornwall County was transferred from New England to Massachusetts in 1692 and called Yorkshire. Much of this region became part of Maine when that state was admitted in 1820.
- Williamson, William D. (1832). The History of the State of Maine: From Its First Discovery, 1602, to the Separation, A. D. 1820, Inclusive. Vol. I. Hallowell, Maine: Glazier, Masters & Company. p. 421.
- Williamson, William D. (1832). The History of the State of Maine: From Its First Discovery, 1602, to the Separation, A. D. 1820, Inclusive. Vol. I. Hallowell, Maine: Glazier, Masters & Company. p. 443.
- Reid, John G; Maine, Charles II and Massachusetts: Governmental Relationships in Early Northern New England.; Portland, Maine: Maine Historical Society Research Series Number 1; 1977; Page. 138.
- Massachusetts. Records of the Governor and Company of the Massachusetts Bay in New England.; Vol. 5; Page16.
- Williamson, William D. (1832). The History of the State of Maine: From Its First Discovery, 1602, to the Separation, A. D. 1820, Inclusive. Vol. I. Hallowell, Maine: Glazier, Masters & Company. p. 446.
- New York: Commissioners of Statutory Revision:Colonial Laws of New York from the year 1664 to the Revolution, including the Charters of the Duke of York, the Commissions and instructions to Colonial Governors, the Duke's Laws, the Laws of the Dongan and Leisler Assemblies, the Charters of Albany and New York, and the acts of the Colonial Legislatures from 1691 to 1775, inclusive. Report to the Assembly #107, 1894. five Volumes. Albany, New York; 1894 - 1896.Chapter 4; Volume 1; Page 122.
- Barnes, 69-70; New Hampshire. Laws of New Hampshire, Including Public and Private Acts and Resolves, 1680–1835, 1:166, 171.