The Pelham Islands are a group of islands in western Long Island Sound that belonged to Thomas Pell in the 17th century. The islands, and most of the surrounding area, were purchased from the Siwanoy Indians by Pell in 1654, creating Pelham Manor. This large tract of land would eventually become the present-day Town and Village of Pelham and Pelham Manor, Town of Eastchester, cities of New Rochelle and Mount Vernon in Westchester County, and the Pelham Bay and Eastchester neighborhoods of the Bronx in New York City.

The Siwanoy were an Indigenous American band of Munsee-speaking people, who lived in Long Island Sound along the coasts of what are now The Bronx, Westchester County, New York, and Fairfield County, Connecticut. They were one of the western bands of the Wappinger Confederacy. By 1640, their territory (Wykagyl) extended from Hell Gate to Norwalk, Connecticut, and as far inland as White Plains; it became hotly contested between Dutch and English colonial interests.