Seabrook is a census-designated place in the town of Mashpee in Barnstable County, Massachusetts, United States. The population was 455 at the 2010 census. Seabrook is located in the southern part of the town of Mashpee along its western border at 41°34′55″N 70°29′55″W / 41.58194°N 70.49861°W. It is bounded by the town of Falmouth to th…Seabrook is a census-designated place in the town of Mashpee in Barnstable County, Massachusetts, United States. The population was 455 at the 2010 census. Seabrook is located in the southern part of the town of Mashpee along its western border at 41°34′55″N 70°29′55″W / 41.58194°N 70.49861°W. It is bounded by the town of Falmouth to the west, by Old Ockway Road to the northeast, by a short segment of Red Brook Road and by the Monomoscoy Island CDP to the southeast, and by Hamblin Pond to the south.