New Castle, originally named Fort Casimir, was founded in 1651 by Peter Stuyvesant, who was sent to provide the Dutch with command of all river traffic. Because of its strategic locations, ownership of the settlement was constantly changing. The flags of the Netherlands, Sweden and Great Britain have all flown over New Castle.

The three counties which make up the state of Delaware were added to William Penn's lands in America. In 1682, Penn came ashore at New Castle and took possession, but these counties, which were well established, became dissatisfied with Penn's rule. In 1704, when he granted them a separate legislature, New Castle became the colonial capitol of Delaware. The lively town also briefly served as the first state capitol, and continued as the county seat until the 1880's.

Today, just outside the city limits are the New Castle County Airport, Wilmington College, and the Delaware Memorial Bridge.