DeWitt was born in Kingston, New York, the eldest son of Johannes and Mary DeWitt. DeWitt attended school in Kingston and pursued classical studies. He helped his family operate a flour mill in Greenkill. The first mill at the site was built by Mattys Mattysen Van Keuren in 1677. Van Keuren had no children and when he died the mill was passed on to his nephew, who was a DeWitt.
Political career
He was first elected to New York'sColonial Assembly to represent Ulster County in 1768. He was returned to that seat in every election until the Assembly was replaced in the American Revolution by a Provisional Congress for the colony in 1775. That year he was one of the members who voted to approve the work of the Continental Congress. As the revolution drew near, and the Ulster militia was expanded, he was named Colonel of the 2nd Ulster Militia regiment on December 21, 1775. DeWitt served in the New York Provincial Congress from 1775-1777 while continuing his militia duties. In the New York Provincial Congress he served on the committee that drafted the state's first constitution. He also served on the Committee of Safety. After active warfare slowed, he was elected to the New York Assembly under the new government. He served in the assembly from 1781-1785 and 1785-1787. The assembly sent him as a delegate to the Continental Congress in 1781 and 1784. DeWitt supplied a great deal of flour to the Continental Army from his grist mill on the Greenkill. He died on August 27, 1787 in Kingston and is interred in the Dutch Reformed Cemetery in Hurley, New York. He wrote his will on July 7, 1776 as he prepared to set out for the defense of New York City. He left the mill to his son Gerret, who expanded it in 1806, and the water-powered mill would continue in operation until 1922.
Family life
DeWitt married Blandina DuBois on December 20, 1754 in Hurley, New York. The couple had five children, Johannes Charles DeWitt, Margrietje DeWitt, Maria DeWitt, Gerret DeWitt and Ann DeWitt. DeWitt's grandson Charles G. DeWitt served in the U.S. Congress.