The Territory of Sagadahock, also called the Sagadahoc Colony and New Castle, was an English colonial territory which included the eastern part of what was later colonial Maine and was more sparsely settled than the western region. The area included was east of the Kennebec River.
On some accounts, the English first settled Sagadahoc in 1608–09.
A part of the grant of King Charles II in 1664 to his brother the Duke of York included the territory between the St Croix and Pemaquid and northward, variously called the "Sagadahoc Territory" and "New Castle".
The area was later absorbed into the Province of Maine. In 1691, a new charter of Massachusetts was granted by William III and Mary II and included the Province of Maine, the "territory of Sagadahoc", and also Nova Scotia.
- Henry Otis Thayer, The Sagadahoc colony, comprising the relation of a voyage into New England (1970), pp. 76, 215: "But another opinion assigns English residents or a fishing company to Sagadahoc in 1608-9, after Popham's men..."
- Charlton Thomas Lewis, Harper's book of facts: a classified encyclopædia (1906)
- Samuel Hazard, Hazard's United States commercial and statistical register, vol. 3 (1841), p. 201: "We have endeavored to show that the claims of the colony of Massachusetts Bay to extend its territory to the St. Lawrence, in virtue of the grant of the Sagadahoc country by Charles II to the Duke of York in 1664..."
- House of Commons papers, vol. 61 (1843), p. 85