In early Dutch maps of the American colonies from the early 17th century, the term Mattabeseck is applied to an 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.
Although the Dutch used the term broadly, specifically speaking, Mattabeseck is a place name for the location known today as Middletown, Connecticut. Linguistically, Mattabeseck is a regional variant of the same word as Mattapoisett, and means "land between waters". It was used in both instances to indicate a place of portage. In this instance, the portage refers to the trail connecting the Quinnipiac River in Meriden to the Mattabeseck River (today known as the Mattabesset River[1]) in Middletown, and which subsequently links to the Connecticut River. In other words, travelling south on the Connecticut, at Middletown the river turns to the southeast toward the mouth of the Connecticut, but, by taking the Mattabesset River and then portaging (roughly along the route of today's Route 66), one can connect to the Quinnipiac River and reach Long Island Sound at New Haven Harbor.
For the first few years of its existence, the town of Middletown was named Mattabeseck, which was laid out on the broad hill south of the mouth of the Mattabeseck swamplands in 1647 and afterwards.
The Mattabesset River as delineated on present-day maps flows out of Harts Ponds in the town of Berlin and travels 16.1 miles (25.9 km) east to the Connecticut River, passing Kensington and later forming the boundary between Middletown and Cromwell.[2]
Further south, the Coginchaug River (or "winding meadow") flows from an upland meadow in Durham, northwards to the Mattabesset just upstream of that river's junction with the Connecticut. This river was the route to the portage place, located near Palmer Field, just below Sowheag's main stronghold at Indian Hill. Since it was the old western boundary of the incorporated City of Middletown, it was also called the West River, and also, for no known reasons, it was given other names, including the Sebethe River and the Arrawanna River. Presumably the word Mattabeseck was never considered properly euphonious, and various local individuals tried to improve on the name poetically.
Mattabeseck is also the name of the indigenous people who lived along the river. For more information see article under Mattabesset.