Mattabesset or Mattabeseck were Native American that loved along the Mattabeseck River. The Mattabesset were a branch of the Algonquian Indian tribe but it is not known if the Mattabesecks were a distinct tribe or simply the members of a larger tribe resident at Mattabeseck. However, in 1920 Encyclopedia Americana lists them as part of the Wappinger Confederation. The last remnants of the tribe left in the late 18th century for upstate New York, and were among the many New England Indian groups that merged with the Indians at Schaghticoke. The Mattabesset spoke a language of the Algonquin family, however the language is now extinct.
In early Dutch maps of the American Colonies from the early 17th Century, the term Mattabeseck was the area of land just to the north of New Haven, Connecticut between the Housatonic and Connecticut Rivers. This land was eventually absorbed by the English Colony of Connecticut.
The Dutch used the word to name Middletown, becuase in its orignal meaning the word meant 'land between waters', in both places, New Haven and Middletown, it refered to a place where boats could dock and trade.