The town of Riverhead is in Suffolk County, New York, on the north shore of Long Island. The population was 33,506 at the 2010 census. The town is on the mouth of the Peconic River, for which the town is named. Riverhead has been the county seat of Suffolk County since 1727. Riverhead contains the smaller hamlet of Riverhead, which includes the town's principal commercial downtown.
European colonists purchased the 'Southold land' from the local Algonquian-speaking Native Americans and Shinnecock Indian Nation in 1649. An additional portion was purchased from Col. William Smith and divided among settlers in 1742.
The town of Riverhead was created in 1792 as part of new jurisdictions after the American Revolution. The New York State Legislature divided it from the town of Southold, New York, which lies to the north and east. Riverhead was separated at the behest of its inhabitants, who "represented to the Legislature that their town is so long that it is very inconvenient for them [people of western regions of Southold] to attend at town meetings, and also to transact the other necessary business of the said town, and have prayed that the same may be divided into two towns". The poor western sections of Southold, with no harbor and little commerce, were thus divided. On March 13, 1792, the Legislature passed a bill splitting off this section under the name River Head. The new enclave's first town meeting was scheduled to be held April 3, 1792.
By 1902, its approximate population was 2,500.