High Quality Content by WIKIPEDIA articles! Mattabesset or Mattabeseck refers to the Native American group which had its principal settlement at the Mattabeseck River of what is today Connecticut, United States. It is presumed that the portage offered the Mattabeseck additional opportunities for trade. The Mattabeseck River also forms an extensive swamplands where it meets the Connecticut, which would also have offered a variety of natural resources for exploitation.