On December 12, 1774, in Burlington, he was married by a civil magistrate to Elizabeth Fenimore, daughter of Richard Fenimore, a Quaker of Rancocas.
Career
During the early 1780s, Cooper became a storekeeper in Burlington, New Jersey, located along the Delaware River. By the end of the decade, he was a successful land speculator and wealthy frontier developer in what is now Otsego County, New York. Soon after the conclusion of the Revolutionary War, he acquired a tract of land several thousand acres in extent within the borders of New York state and lying along the head waters of the Susquehanna River at Otsego Lake. He founded the Village of Otsego at the foot of the lake in 1786, creating a traditional plan for the village inspired by that of Burlington. He moved his family there, arriving on 10 November 1790. The judge and other investors also founded De Kalb, New York, near the east end of Lake Ontario and the St. Lawrence River, in 1803, platting approximately 64,000 acres and selling the parcels on. His brother James took care of the holdings, which were tied up in litigation for years, both before and after the death of Judge Cooper in 1809. The Cooper family holdings were all gone by 1817. In 1852 a village was named Cooper's Falls north of De Kalb. James stayed in the area, and his son William grew up in De Kalb and was a carpenter. The existing De Kalb Historical Society building was built by the judge's nephew, William, and some of his descendants may still live in the area. After 1791, when Otsego County was split off from Montgomery County, Cooper was appointed as a county judge. He was later elected to two terms in Congress, representing the Federalist Party in the 4th and the 6th United States Congresses. In 1796, Cooper determined to make his home permanently in the town he had founded, which by that time promised to become a thriving settlement. It attracted many land-hungry migrants from New England. He began the construction of a mansion, completed in 1799, which he named Otsego Hall. For many years it served as his manor house; it was by far the most spacious and stately private residence in central New York. Cooper family tradition has it that Judge Cooper was killed by a blow to the head sustained during an argument with a political opponent after a public meeting in Albany, New York on December 22, 1809. No evidence of this can be found, and the story appeared to arise in 1897. A great-grandson of the judge published this account, which historians consider implausible. They believe that Judge Cooper died of natural causes. Cooper was buried at the Episcopal Christ Churchyard in Cooperstown. His son James Fenimore Cooper, a popular author of historical novels, was buried there many years later. A great-grandson, Paul F. Clark, became a NebraskaState Representative. A 2xgreat-grandson, writer Paul Fenimore Cooper, is known for the children's adventure, .
Legacy and honors
Cooperstown was named for him, as he was the founder.