[2] Situated at the mouth of the Peconic River, which empties into Peconic Bay where the North and South Forks of Long Island split, the town of Riverhead (of which the CDP is a part) is the official county seat of Suffolk County.

The hamlet began with the Suffolk County Court House, a 1727 structure built to serve both the North and South Forks.

Since that year, Riverhead has served as the seat of Suffolk County, and still contains the primary courts of the region.

Riverhead's downtown area formed as an active commercial hub during the 19th century.

The hamlet contains the principal downtown area in the Town of Riverhead and one of the largest in Suffolk County.

Outside of this downtown area are rural sections which contain both active farms and residential developments.

[10] It is owned by East End Local Media Corp., an independent company based in Riverhead.

WCBS-TV (DRT channel 22), a broadcast relay station, is also licensed to Riverhead.