The Newcastle CDP is in the eastern part of the town of Newcastle in central Lincoln County. The CDP is on the west bank of the Damariscotta River, which forms the boundary with the town of
Damariscotta. The CDP extends south down the river to a location north of Little Point, and north upriver and along Salt Bay to Damariscotta Mills and the outlet of
Damariscotta Lake. Starting at its southern point on the Damariscotta River, the western boundary of the CDP follows Schrafft Road, River Road, an unnamed stream, a powerline, Old County Road, Kavanagh Road, Academy Road and Pond Road (
Maine State Route 215) to Damariscotta Lake. US Route 1 passes through the community, leading northeast to
Rockland and southwest to
Bath.
Portland is to the southwest.
U.S. Route 1 Business splits off US 1 to run through the centers of Newcastle and Damariscotta as Main Street.
Maine Route 215 has its southern terminus at US 1 Business in Newcastle and leads north to
ME 32 in the northern part of the town of
Jefferson. According to the
United States Census Bureau, the Newcastle CDP has a total area of , of which are land and , or 22.41%, are water. ==Demographics==