New Castle County, Delaware On November 6, 1674, New Amstel was made dependent on New York Colony, and was renamed New Castle on November 11, 1674. On September 22, 1676, New Castle County was formally placed under the Duke of York's laws. It gained land from Upland County on November 12, 1678. On June 21, 1680, St. Jones County was carved from New Castle County. It is known today as Kent County, Delaware. On August 24, 1682, New Castle County, along with the rest of the surrounding land, was transferred from the Colony of New York to the possession of William Penn, who established
New Castle County, Delaware James, was granted this land by King Charles II. One of the first acts by the Duke was to order removal of all Dutch from New Amsterdam; he renamed New Amstel as New Castle. In 1672, the town of New Castle was incorporated and English law ordered. However, in 1673, the Dutch attacked the territory, reclaiming it for their own. On September 12, 1673, the Dutch established New Amstel in present-day Delaware, fairly coterminous with today's New Castle County. The establishment was not stable, and it was transferred to the British under the Treaty of Westminster on February 9, 1674.