According to the United States Census Bureau, the town has a total area of 32.6 square miles (84.4 km²), of which, 29.0 square miles (75.1 km²) of it is land and 3.6 square miles (9.3 km²) of it (11.02%) is water. Newcastle is situated beside the Damariscotta River.

The town is crossed by U. S. Route 1 and state routes 194 and 215. It borders the towns of Jefferson to the north, Edgecomb to the south, and Alna to the northwest. Separated by water, it is near the towns of Wiscasset to the southwest, and Nobleboro, Damariscotta, Bristol and South Bristol to the east.

Newcastle Area Code is 207

• Town of Newcastle, ME - P.O. Box 386 (4 Pump Street), Newcastle, ME 04553
  Telephone: 207-563-3441 Fax: 207-563-6995
• The Newcastle Historical Society: Established in 1998, The Newcastle Historical Society provides visitors with a doorway to the past at its museum in the old historic Taniscot Engine House located on Main Street. There, visitors will find our museum filled with artifacts and historical memorabilia of the heritage of the people that live and have lived within its boundaries.
  - P.O. Box 482, Newcastle, Me 04553
• The Harbor View Inn: The Harbor View Inn is a restored New England Cape sitting on a knoll above Main Street in Newcastle.
  - P.O. Box 791, Newcastle, Maine 04553
  Telephone: 207-563-2900
• Newcastle Inn: The Newcastle Inn located in the heart of of MidCoast Maine. This historic country inn, with wonderful views of the Damariscotta River, has spacious common areas (including a private pub just for guests), complimentary WiFi and a guest pantry with complimentary beverages, snacks and a bottomless cookie jar with made-from-scratch cookies.
  - 60 River Road, Newcastle, Maine 04553
  Telephone: 207-563-5685