Known for his 1783 deliverance of the Treaty of Paris, Delafield would settle in New York City, achieving further financial prosperity there.

Arriving in New York City in the spring of 1783, while it was still under British control, he brought with him the first copy of the provisional treaty of peace between the United States and Great Britain.

[1][2][3] He was said to have arrived with significant wealth, holding the title of “Count of the Holy Roman Empire” by descent, and by the turn of the century, had become one of New York’s wealthiest individuals, earning the title "one of the fathers of Wall Street."

His mansion, located across the East River from New York City, was a grand estate where he lived with his wife, Ann Hallett—herself from a notable Revolutionary family—and their eleven children.

Together, they lived at 16 Wall Street in New York City, and were the parents of eleven children, including:[7] His summer residence, on 140-acres, built in 1791 on the East River opposite Blackwell's Island, was known as" Sunswick" and was one of the largest and best appointed private houses near New York.